How aneuploidy affects metabolic control and causes cancer

The complexity and diversity of cancer-specific phenotypes, including de-differentiation, invasiveness, metastasis, abnormal morphology and metabolism, genetic instability and progression to malignancy, have so far eluded explanation by a simple, coherent hypothesis. However, an adaptation of Metabolic Control Analysis supports the 100-year-old hypothesis that aneuploidy, an abnormal number of chromosomes, is the cause of cancer. The results demonstrate the currently counter-intuitive principle that it is the fraction of the genome undergoing differential expression, not the magnitude of the differential expression, that controls phenotypic transformation. Transforming the robust normal phenotype into cancer requires a twofold increase in the expression of thousands of normal gene products. The massive change in gene dose produces highly non-linear (i.e. qualitative) changes in the physiology and metabolism of cells and tissues. Since aneuploidy disrupts the natural balance of mitosis proteins, it also explains the notorious genetic instability of cancer cells as a consequence of the perpetual regrouping of chromosomes. In view of this and the existence of non-cancerous aneuploidy, we propose that cancer is the phenotype of cells above a certain threshold of aneuploidy. This threshold is reached either by the gradual, stepwise increase in the level of aneuploidy as a consequence of the autocatalysed genetic instability of aneuploid cells or by tetraploidization followed by a gradual loss of chromosomes. Thus the initiation step of carcinogenesis produces aneuploidy below the threshold for cancer, and the promotion step increases the level of aneuploidy above this threshold. We conclude that aneuploidy offers a simple and coherent explanation for all the cancer-specific phenotypes. Accordingly, the gross biochemical abnormalities, abnormal cellular size and morphology, the appearance of tumour-associated antigens, the high levels of secreted proteins responsible for invasiveness and loss of contact inhibition, and even the daunting genetic instability that enables cancer cells to evade chemotherapy, are all the natural consequence of the massive over- and under-expression of proteins.

Dominant transformation by mutated human ras genes in vitro requires more than 100 times higher expression than is observed in cancers

The gene-mutation-cancer hypothesis holds that mutated cellular protooncogenes, such as point-mutated proto-ras, "play a dominant part in cancer," because they are sufficient to transform transfected mouse cell lines in vitro [Alberts, B., Bray, D., Lewis, J., Raff, M., Roberts, K. & Watson, J. D. (1994) Molecular Biology of the Cell (Garland, New York)]. However, in cells transformed in vitro mutated human ras genes are expressed more than 100-fold than in the cancers from which they are isolated. In view of the discrepancy between the very low levels of ras transcription in cancers and the very high levels in cells transformed in vitro, we have investigated the minimal level of human ras expression for transformation in vitro. Using point-mutated human ras genes recombined with different promoters from either human metallothionein-IIA or human fibronectin or from retroviruses we found dominant in vitro transformation of the mouse C3H cell line only with ras genes linked to viral promoters. These ras genes were expressed more than 120-fold higher than are native ras genes of C3H cells. The copy number of transfected ras genes ranged from 2-6 in our system. In addition, nondominant transformation was observed in a small percentage (2-7%) of C3H cells transfected with ras genes that are expressed less than 20 times higher than native C3H ras genes. Because over 90% of cells expressing ras at this moderately enhanced level were untransformed, transformation must follow either a nondominant ras mechanism or a non-ras mechanism. We conclude that the mutated, but normally expressed, ras genes found in human and animal cancers are not likely to "play a dominant part in cancer." The conclusion that mutated ras genes are not sufficient or dominant for cancer is directly supported by recent discoveries of mutated ras in normal animals, and in benign human tissue, "which has little potential to progress" [Jen, J., Powell, S. M., Papadopoulos, N., Smith, K. J., Hamilton, S. R., Vogelstein, B. & Kinzler, K. W. (1994) Cancer Res. 54, 5523-5526]. Even the view that mutated ras is necessary for cancer is hard to reconcile with (i) otherwise indistinguishable cancers with and without ras mutations, (ii) metastases of the same human cancers with and without ras mutations, (iii) retroviral ras genes that are oncogenic without point mutations, and (iv) human tumor cells having spontaneously lost ras mutation but not tumorigencity.

DNA recombination is sufficient for retroviral transduction

Oncogenic retroviruses carry coding sequences that are transduced from cellular protooncogenes. Natural transduction involves two nonhomologous recombinations and is thus extremely rare. Since transduction has never been reproduced experimentally, its mechanism has been studied in terms of two hypotheses: (i) the DNA model, which postulates two DNA recombinations, and (ii) the RNA model, which postulates a 5' DNA recombination and a 3' RNA recombination occurring during reverse transcription of viral and protooncogene RNA. Here we use two viral DNA constructs to test the prediction of the DNA model that the 3' DNA recombination is achieved by conventional integration of a retroviral DNA 3' of the chromosomal protooncogene coding region. For the DNA model to be viable, such recombinant viruses must be infectious without the purportedly essential polypurine tract (ppt) that precedes the 3' long terminal repeat (LTR) of all retroviruses. Our constructs consist of a ras coding region from Harvey sarcoma virus which is naturally linked at the 5' end to a retroviral LTR and artificially linked at the 3' end either directly (construct NdN) or by a cellular sequence (construct SU) to the 5' LTR of a retrovirus. Both constructs lack the ppt, and the LTR of NdN even lacks 30 nucleotides at the 5' end. Both constructs proved to be infectious, producing viruses at titers of 10(5) focus-forming units per ml. Sequence analysis proved that both viruses were colinear with input DNAs and that NdN virus lacked a ppt and the 5' 30 nucleotides of the LTR. The results indicate that DNA recombination is sufficient for retroviral transduction and that neither the ppt nor the complete LTR is essential for retrovirus replication. DNA recombination explains the following observations by others that cannot be reconciled with the RNA model: (i) experimental transduction is independent of the packaging efficiency of viral RNA, and (ii) experimental transduction may invert sequences with respect to others, as expected for DNA recombination during transfection.

The toxicity of azidothymidine (AZT) on human and animal cells in culture at concentrations used for antiviral therapy

AZT, a chain terminator of DNA synthesis originally developed for chemotherapy, is now prescribed as an anti-human immunodeficiency virus (HIV) drug at 500 to 1500 mg/person/day, which corresponds to 20 to 60 microM AZT. The human dosage is based on a study by the manufacturer of the drug and their collaborators, which reported in 1986 that the inhibitory dose for HIV replication was 0.05 to 0.5 microM AZT and that for human T-cells was 2000 to 20,000 times higher, i.e. 1000 microM AZT. This suggested that HIV could be safely inhibited in humans at 20 to 60 microM AZT. However, after the licensing of AZT as an anti-HIV drug, several independent studies reported 20- to 1000-fold lower inhibitory doses of AZT for human and animal cells than did the manufacturer's study, ranging from 1 to 50 microM. In accord with this, life threatening toxic effects were reported in humans treated with AZT at 20 to 60 microM. Therefore, we have re-examined the growth inhibitory doses of AZT for the human CEM T-cell line and several other human and animal cells. It was found that at 10 microM and 25 microM AZT, all cells are inhibited at least 50% after 6 to 12 days, and between 20 and 100% after 38 to 48 days. Unexpectedly, variants of all cell types emerged over time that were partially resistant to AZT. It is concluded that AZT, at the dosage prescribed as an anti-HIV drug, is highly toxic to human cells.

Foreign-protein-mediated immunodeficiency in hemophiliacs with and without HIV

Hemophilia-AIDS has been interpreted in terms of two hypotheses: the foreign-protein-AIDS hypothesis and the Human Immunodeficiency Virus (HIV)-AIDS hypothesis. The foreign-protein-AIDS hypothesis holds that proteins contaminating commercial clotting factor VIII cause immunosuppression. The foreign-protein hypothesis, but not the HIV hypothesis, correctly predicts seven characteristics of hemophilia-AIDS: 1) The increased life span of American hemophiliacs in the two decades before 1987, although 75% became infected by HIV--because factor VIII treatment, begun in the 1960s, extended their lives and simultaneously disseminated harmless HIV. After 1987 the life span of hemophiliacs appears to have decreased again, probably because of widespread treatment with the cytotoxic anti-HIV drug AZT. 2) The distinctly low, 1.3-2%, annual AIDS risk of hemophiliacs, compared to the higher 5-6% annual risk of intravenous drug users and male homosexual aphrodisiac drug users--because transfusion of foreign proteins is less immunosuppressive than recreational drug use. 3) The age bias of hemophilia-AIDS, i.e. that the annual AIDS risk increased 2-fold for each 10-year increase in age--because immunosuppression is a function of the lifetime dose of foreign proteins received from transfusions. 4) The restriction of hemophilia-AIDS to immunodeficiency diseases--because foreign proteins cannot cause non-immunodeficiency AIDS diseases, like Kaposi's sarcoma. 5) The absence of AIDS diseases above their normal background in sexual partners of hemophiliacs--because transfusion-mediated immunotoxicity is not contagious. 6) The occurrence of immunodeficiency in HIV-free hemophiliacs--because foreign proteins, not HIV, suppress their immune system. 7) Stabilization, even regeneration, of immunity of HIV-positive hemophiliacs by long-term treatment with pure factor VIII. This shows that neither HIV nor factor VIII plus HIV are immunosuppressive by themselves. Therefore, AIDS cannot be prevented by elimination of HIV from the blood supply and cannot be rationally treated with genotoxic antiviral drugs, like AZT. Instead, hemophilia-AIDS can be prevented and has even been reverted by treatment with pure factor VIII.

HIV as a surrogate marker for drug use: a re-analysis of the San Francisco Men's Health Study

Our analysis of drug use and morbidity data from a cohort of 1034 men yields the following results: 1) HIV infection is a strong indicator of drug use-HIV-positive respondents reported an average lifetime dose of recreational drugs (excluding marijuana) 2.3 times higher than HIV-negative respondents. 2) Homosexuality is a strong indicator of drug use-homosexual respondents reported an average lifetime dose 2.0 times higher than heterosexual respondents. 3) The incidence of AIDS-defining diseases was not limited to respondents infected with HIV, but was almost completely limited (98%) to respondents who reported using drugs. We also address a previous report (Ascher et al., 1993) that was based on the same database and purported to show that HIV alone correlates with the development of AIDS. Specifically, we show that the relationship between HIV infection and CD4+ T Cell loss is weaker than reported by Ascher et al., and provides little evidence for a causative relationship. These results support the hypothesis that long-term, habitual drug use can cause the conditions known as AIDS (independent of the presence of HIV), and refute the hypothesis that HIV alone causes these conditions independent of drug use.

Development of transforming function during transduction of proto-ras into Harvey sarcoma virus

Oncogenic retroviruses are generated by transduction of the coding region of a protooncogene and acquire genetic changes during subsequent replication. Critical genetic events which occurred during and after transduction of rat proto-ras-1Ha into Harvey sarcoma virus were identified by evaluating the transforming activity of plausible synthetic progenitor proviruses encompassing the complete proto-ras genomic region with or without various 5' deletions. All progenitor proviruses induced phenotypic transformation of mouse NIH 3T3 cells, although with a 5- to 10-fold lower frequency than Harvey sarcoma provirus. Although no tumor formation was observed in vivo after inoculation in the absence of helper murine retrovirus, both wild-type and progenitor viruses inoculated in the presence of helper virus induced tumors in newborn BALB/c mice. No critical alterations of the p21ras coding region and no deletion of 5' genomic elements were detected in a progenitor virus encompassing the complete proto-ras genomic region that had been isolated from tumors. However, one progenitor virus that included all proto-ras exons induced tumors with a decreased latency. This virus contained a mutation in codon 12 (glycine to valine), which had apparently been selected during tumorigenesis in vivo. During the genesis of Harvey sarcoma virus, critical steps conferring transforming function are therefore transduction of coding proto-ras exons and enhancement of their transforming function by specific amino acid changes in p21ras.

The role of drugs in the origin of AIDS

It is proposed that the new American and European AIDS epidemics are caused by recreational and anti-HIV drugs rather than by human immunodeficiency virus (HIV). Chronologically, the AIDS epidemic in the 1980s followed a massive escalation in the consumption of recreational drugs that started in the 1960s and 70s. Epidemiologically, both epidemics derive about 80% of their victims from the same groups of 20-44 year-olds, of which 90% are males. In America 32% of these are intravenous drug users and their children, about 60% are male homosexuals who are long-term users of oral aphrodisiac drugs and an unknown percentage are prescribed the cytotoxic DNA chain terminator AZT, as inhibitor of HIV. Direct evidence indicates that these drugs are necessary for HIV-positives and sufficient for HIV-negatives to develop AIDS diseases. The drug-AIDS hypothesis predicts correctly that: (i) AIDS is new in the US, because the drug epidemic is new, while the HIV epidemic is old--fixed at a constant 1 million Americans since 1985; (ii) despite an increase in venereal diseases, AIDS remains restricted to long-term drug users and small groups with clinical deficiencies; (iii) over 72% of AIDS occurs in 20-44 year-old males, because they make up over 80% of hard psychoactive drug use; (iv) distinct AIDS diseases correlate with the use of distinct drugs, eg Kaposi's sarcoma with nitrite inhalants, tuberculosis with intravenous drugs, and leukopenia, anemia, and nausea with AZT; (v) AIDS diseases are only acquired after long-term drug consumption, rather than after single contacts as the virus-hypothesis predicts. The drug hypothesis can be tested epidemiologically and experimentally in animals. It predicts that most AIDS can be prevented by stopping the consumption of drugs, and provides a rational basis for therapy.

AIDS acquired by drug consumption and other noncontagious risk factors

The hypothesis that human immunodeficiency virus (HIV) is a new, sexually transmitted virus that causes AIDS has been entirely unproductive in terms of public health benefits. Moreover, it fails to predict the epidemiology of AIDS, the annual AIDS risk and the very heterogeneous AIDS diseases of infected persons. The correct hypothesis must explain why: (1) AIDS includes 25 previously known diseases and two clinically and epidemiologically very different epidemics, one in America and Europe, the other in Africa; (2) almost all American (90%) and European (86%) AIDS patients are males over the age of 20, while African AIDS affects both sexes equally; (3) the annual AIDS risks of infected babies, intravenous drug users, homosexuals who use aphrodisiacs, hemophiliacs and Africans vary over 100-fold; (4) many AIDS patients have diseases that do not depend on immunodeficiency, such as Kaposi's sarcoma, lymphoma, dementia and wasting; (5) the AIDS diseases of Americans (97%) and Europeans (87%) are predetermined by prior health risks, including long-term consumption of illicit recreational drugs, the antiviral drug AZT and congenital deficiencies like hemophilia, and those of Africans are Africa-specific. Both negative and positive evidence shows that AIDS is not infectious: (1) the virus hypothesis fails all conventional criteria of causation; (2) over 100-fold different AIDS risks in different risk groups show that HIV is not sufficient for AIDS; (3) AIDS is only 'acquired,' if at all, years after HIV is neutralized by antibodies; (4) AIDS is new but HIV is a long-established, perinatally transmitted retrovirus; (5) alternative explanations disprove all assumptions and anecdotal cases cited in support of the virus hypothesis; (6) all AIDS-defining diseases occur in matched risk groups, at the same rate, in the absence of HIV; (7) there is no common, active microbe in all AIDS patients; (8) AIDS manifests in unpredictable and unrelated diseases; and (9) it does not spread randomly between the sexes in America and Europe. Based on numerous data documenting that drugs are necessary for HIV-positives and sufficient for HIV-negatives to develop AIDS diseases, it is proposed that all American/European AIDS diseases, that exceed their normal background, result from recreational and anti-HIV drugs. African AIDS is proposed to result from protein malnutrition, poor sanitation and subsequent parasitic infections. This hypothesis resolves all paradoxes of the virus-AIDS hypothesis. It is epidemiologically and experimentally testable and provides a rational basis for AIDS control.

Transforming function of proto-ras genes depends on heterologous promoters and is enhanced by specific point mutations

Based on transfection into cells in culture or natural transduction into retroviruses, proto-ras genes seem to derive transforming function either from heterologous promoters or from point mutations. Here we ask how such different events could achieve the same results. To identify homologous regulatory elements, about 3 kilobases of rat DNA upstream of the first untranslated proto-Ha-ras exon was sequenced. Surprisingly, the sequence shares at -1858 a homology of 148 nucleotides with Harvey (Ha) sarcoma virus, 5' of viral ras, signaling possibly a second untranslated proto-Ha-ras exon. In addition the sequence contains a perfect repeat of 25 CA dinucleotides at -2655. A retroviral promoter, even from upstream of the poly(CA), conferred transforming function on proto-Ha-ras and increased transcription greater than 100-fold compared with that of unrearranged proto-ras. Point mutations were not necessary for transforming function of rat and human proto-Ha-ras genes with retroviral promoters but did enhance it greater than 10-fold. A unifying hypothesis proposes that proto-ras genes depend on high expression from heterologous promoters or enhancers for transforming function, which is modulated by ras point mutations. The hypothesis makes two testable predictions. (i) Unrearranged proto-ras genes with point mutations, which occur in some cancers, have no transforming function. Indeed, tumors with mutated proto-ras genes, even those that also lack hypothetical tumor-suppressor genes, are indistinguishable from counterparts with normal proto-ras genes. (ii) Proto-ras genes in transfected cells derive transforming function from heterologous promoters or enhancers acquired via illegitimate recombination from vector DNAs and particularly from viral helper genes that must be cotransfected for transformation of primary cells. Indeed, expression of exogenous proto-ras genes in cells transformed by transfection is as high as for viral ras genes and is much higher than in the cells of origin.

A retroviral promoter is sufficient to convert proto-src to a transforming gene that is distinct from the src gene of Rous sarcoma virus

The src genes of four natural isolates of avian sarcoma viruses differ from cellular proto-src in two genetic substitutions: the promoter of the cellular gene is replaced by a retroviral counterpart, and at least six codons from the 3' terminus are replaced by retroviral or heterologous cell-derived elements. Since virus constructs with a complete proto-src coding region failed to transform avian cells but acquired transforming function by point mutations of various codons, it has been proposed that point mutation is sufficient to convert proto-src to a transforming gene. However, promoter substitution is sufficient to convert two other proto-onc genes, proto-ras and proto-myc, to retroviral transforming genes. In view of this, we have reexamined whether promoter substitution, point mutation, or both are necessary to convert proto-src into a retroviral transforming gene. It was found that a recombinant virus (RpSV), in which the src gene of Rous sarcoma virus (RSV) was replaced by the complete coding region of proto-src, transformed quail and chicken embryo cells. The oncogene of RpSV differs from the src gene of RSV in three genetic properties: (i) it is weaker--e.g., transformed cells are flatter; (ii) it is slower--e.g., focus formation takes 9 to 12 days compared to 4 days for RSV; and (iii) its host range is narrower than that of RSV--e.g., only subsets of heterogeneous embryo cells are transformed by RpSV even after weeks or months. Replacement of the proto-src 3' terminus of RpSV by that of src from RSV generates a recombinant virus (RpvSV) that equals RSV in transforming function. It is concluded that a retroviral promoter, naturally substituted via illegitimate recombination with retroviruses, is sufficient to convert at least three proto-onc genes, src, myc, and ras, to retroviral transforming genes.

Evidence that retroviral transduction is mediated by DNA not by RNA

Retroviral transduction of cellular nucleic acid sequences requires illegitimate RNA or DNA recombination. To test a model that postulates transduction via efficient illegitimate recombination during reverse transcription of viral and cellular RNAs, we have measured the ability of Harvey sarcoma viruses (HaSVs) with artificial 3' termini to recover a retroviral 3' terminus from helper Moloney virus (MoV) by illegitimate and homologous recombination. For this purpose, mouse NIH 3T3 cells were transformed with Harvey proviruses and then superinfected with MoV. The proviruses lacked the 3' long terminal repeat and an untranscribed region of the 5' long terminal repeat to prevent virus regeneration from input provirus. Only 0-11 focus-forming units of HaSV were generated upon MoV superinfection of 3 x 10(6) cells transformed by Harvey proviruses with MoV-unrelated termini. This low frequency is consistent with illegitimate DNA recombination via random Moloney provirus integration 3' of the transforming viral ras gene in the 10(6)-kilobase mouse genome. When portions of murine viral envelope (env) genes were attached 3' of ras, 10(2)-10(5) focus-forming units of HaSV were generated, depending on the extent of homology with env of MoV. These recombinants all contained HaSV-specific sequences 5' and MoV-specific sequences 3' of the common env homology. They were probably generated by recombination during reverse transcription rather than by recombination among either input or secondary proviruses, since (i) the yield of recombinants was reduced by a factor of 10 when the env sequence was flanked by splice signals and (ii) HaSV RNAs without retroviral 3' termini would be inadequate templates for provirus synthesis. We conclude that there is no efficient illegitimate recombination in retroviruses. In view of known precedents of illegitimate DNA recombination, the structure of known viral onc genes, and our evidence for illegitimate DNA recombination via provirus integration, we favor the DNA model of transduction over the RNA model.

Retroviral recombination during reverse transcription

After mixed infection, up to half of related retroviruses are recombinants. During infection, retroviral RNA genomes are first converted to complementary DNA (cDNA) and then to double-stranded DNA. Thus recombination could occur during reverse transcription, by RNA template switching, or after reverse transcription, by breakage and reunion of DNA. It has not been possible to distinguish between these two potential mechanisms of recombination because both single-stranded cDNA and double-stranded proviral DNA exist in infected cells during the eclipse period. Therefore we have analyzed for recombinant molecules among cDNA products transcribed in vitro from RNA of disrupted virions. Since recombinants from allelic parents can only be distinguished from parental genomes by point mutations, we have examined the cDNAs from virions with distinct genetic structures for recombinant-specific size and sequence markers. The parents share a common internal allele that allows homology-directed recombination, but each contains specific flanking sequences. One parent is a synthetically altered Harvey murine sarcoma virus RNA that lacks a retroviral 3' terminus but carries a Moloney murine retrovirus-derived envelope gene (env) fragment 3' of its transforming ras gene. The other parent is intact Moloney virus. Using a Harvey-specific 5' primer and a Moloney-specific 3' primer, we have found recombinant cDNAs with the polymerase chain reaction, proving directly that retroviruses can recombine during reverse transcription unassisted by cellular enzymes, probably by template switching during cDNA synthesis. The recombinants that were obtained in vitro were identical with those obtained in parallel experiments in vivo.

Avian proto-myc genes promoted by defective or nondefective retroviruses are single-hit transforming genes in primary cells

Lymphomas of certain strains of chickens infected by retroviruses frequently contain recombinant transforming genes in which the promoter of the cellular proto-myc gene is replaced by that of a defective rather than an intact retrovirus. Here we ask whether the resulting hybrid genes are sufficient for tumorigenic transformation like viral myc genes. Further, we ask whether retroviruses must be defective in order to mutate proto-myc to a transforming gene or whether the defectiveness plays a transformation-independent function in tumorigenesis. For this purpose the defective provirus of proviral-proto-myc recombinants from lymphomas were repaired, or intact proviruses were recombined with proto-myc genes in vitro, and then compared to recombinant proto-myc genes with defective proviruses for transforming function in quail embryo fibroblasts. It was found that a single copy of a provirus-proto-myc recombinant gene with an intact provirus is sufficient to transform a quail embryo cell in vitro. Moreover, our analyses showed that multiple internal retroviral deletions [corrected] eliminate or inhibit provirus expression. The effect of these deletions [corrected] was detectable only because the inactive proviruses were linked to the selectable, transforming proto-myc gene marker. It is consistent with our results that proviral defectiveness of recombinant proto-myc genes is necessary in vivo for the clonal growth of a transformed cell into a tumor to escape antiviral immunity. The large discrepancy between the probabilities of provirus insertion and tumorigenesis is suggested to reflect the low probabilities of spontaneous deletion of the provirus and of rare, strain-specific defects of tumor-resistance genes of the host.

Cancer genes by illegitimate recombination

Retroviral onc genes are as yet the only proven cancer genes. They are generated by rare illegitimate recombinations between retroviruses and cellular genes, termed proto-onc genes. The claims that these proto-onc genes cause virus-free cancers upon "activation" by mechanisms that do not alter their germline structure are challenged. Instead, it is proposed that retroviral onc genes and cellular cancer genes are generated de novo by illegitimate recombinations that alter the germline structure of normal genes.

Recombinant BALB and Harvey sarcoma viruses with normal proto-ras-coding regions transform embryo cells in culture and cause tumors in mice

The ras genes of BALB and Harvey sarcoma viruses contain point mutations in codon 12 or codons 12 and 59, relative to proto-ras from normal animal and human cells. By in vitro recombination between cloned rat proto-ras and cloned BALB and Harvey sarcoma proviruses, we constructed recombinant proviruses with normal proto-ras-coding regions. These recombinant proviruses transformed mouse 3T3 cells upon transfection. However, when the transforming efficiencies of proviral DNAs were compared after transfection with helper provirus, recombinant proviruses were 2 to 30 times less efficient than the corresponding wild-type proviruses. Recombinant sarcoma viruses isolated from cells transformed by cloned proviral DNA contained the expected normal ras-coding region. They transformed rat embryo cells and induced erythroblastosis and sarcomas in newborn mice as efficiently as wild-type viruses did. We conclude that conversion of normal proto-ras genes to viral ras genes depends on truncation of normal proto-ras regulatory elements and substitution by retroviral (long terminal repeat) promoters and that the transforming function of long terminal repeat-ras genes is enhanced by point mutations.

Human immunodeficiency virus and acquired immunodeficiency syndrome: correlation but not causation

AIDS is an acquired immunodeficiency syndrome defined by a severe depletion of T cells and over 20 conventional degenerative and neoplastic diseases. In the U.S. and Europe, AIDS correlates to 95% with risk factors, such as about 8 years of promiscuous male homosexuality, intravenous drug use, or hemophilia. Since AIDS also correlates with antibody to a retrovirus, confirmed in about 40% of American cases, it has been hypothesized that this virus causes AIDS by killing T cells. Consequently, the virus was termed human immunodeficiency virus (HIV), and antibody to HIV became part of the definition of AIDS. The hypothesis that HIV causes AIDS is examined in terms of Koch's postulates and epidemiological, biochemical, genetic, and evolutionary conditions of viral pathology. HIV does not fulfill Koch's postulates: (i) free virus is not detectable in most cases of AIDS; (ii) virus can only be isolated by reactivating virus in vitro from a few latently infected lymphocytes among millions of uninfected ones; (iii) pure HIV does not cause AIDS upon experimental infection of chimpanzees or accidental infection of healthy humans. Further, HIV violates classical conditions of viral pathology. (i) Epidemiological surveys indicate that the annual incidence of AIDS among antibody-positive persons varies from nearly 0 to over 10%, depending critically on nonviral risk factors. (ii) HIV is expressed in less than or equal to 1 of every 10(4) T cells it supposedly kills in AIDS, whereas about 5% of all T cells are regenerated during the 2 days it takes the virus to infect a cell. (iii) If HIV were the cause of AIDS, it would be the first virus to cause a disease only after the onset of antiviral immunity, as detected by a positive "AIDS test." (iv) AIDS follows the onset of antiviral immunity only after long and unpredictable asymptomatic intervals averaging 8 years, although HIV replicates within 1 to 2 days and induces immunity within 1 to 2 months. (v) HIV supposedly causes AIDS by killing T cells, although retroviruses can only replicate in viable cells. In fact, infected T cells grown in culture continue to divide. (vi) HIV is isogenic with all other retroviruses and does not express a late, AIDS-specific gene. (vii) If HIV were to cause AIDS, it would have a paradoxical, country-specific pathology, causing over 90% Pneumocystis pneumonia and Kaposi sarcoma in the U.S. but over 90% slim disease, fever, and diarrhea in Africa.(viii) It is highly improbable that within the last few years two viruses (HIV-1 and HIV-2) that are only 40% sequence-related would have evolved that could both cause the newly defined syndrome AIDS. Also, viruses are improbable that kill their only natural host with efficiencies of 50-100%, as is claimed for HIVs. It is concluded that HIV is not sufficient for AIDS and that it may not even be necessary for AIDS because its activity is just as low in symptomatic carriers as in asymptomatic carriers. The correlation between antibody to HIV and AIDS does not prove causation, because otherwise indistinguishable diseases are now set apart only on the basis of this antibody. I propose that AIDS is not a contagious syndrome caused by one conventional virus or microbe. No such virus or microbe would require almost a decade to cause primary disease, nor could it cause the diverse collection of AIDS diseases. Neither would its host range be as selective as that of AIDS, nor could it survive if it were as inefficiently transmitted as AIDS. Since AIDS is defined by new combinations of conventional diseases, it may be caused by new combinations of conventional pathogens, including acute viral or microbial infections and chronic drug use and malnutrition. The long and unpredictable intervals between infection with HIV and AIDS would then reflect the thresholds for these pathogenic factors to cause AIDS diseases, instead of an unlikely mechanism of HIV pathogenesis.

Two autonomous myc oncogenes in avian carcinoma virus OK10

The oncogenic avian retrovirus OK10 has the genetic structure gag-delta pol-myc-delta-env. The myc sequence is transduced from a cellular gene, proto-myc, while gag, pol, and env are essential retrovirus genes. By analogy with other directly oncogenic retroviruses, the specific myc sequence of OK10 is thought to be essential for transforming function. However, unlike the specific sequences of all other transforming retroviruses that encode unique transforming proteins, the myc sequence of OK10 encodes two potential transforming proteins, p58 and p200. p200 is translated from the gag-delta pol-myc region of genomic RNA, while p58 is thought to be translated from the gag leader and the open reading frame of myc via a subgenomic mRNA. In this paper, we ask whether both myc genes of OK10 are autonomous transforming genes. By differentially inactivating the p200 myc gene of OK10 provirus in vitro and analyzing transforming function in quail embryo cells, it was found that mutants expressing only p58 transformed like wild-type OK10. Further, it was shown that p58 with and without the gag leader had transforming function and that p58 of wild-type OK10 is initiated from the gag leader. Mutants expressing only p200 were also transforming but less efficiently than mutants that express only p58. A mutant OK10 virus in which the native frameshift of retroviruses between gag and pol was deleted expressed a shortened p200 (delta p200). Although this virus expressed more delta p200 than wild-type OK10 did, it transformed cells less efficiently. It follows that OK10 expresses two autonomous transforming genes, which is unique among retroviruses with onc genes.

Retroviral transduction of oncogenic sequences involves viral DNA instead of RNA

We have studied whether the origin of retroviral onc genes, by transduction of sequences from cellular proto-onc genes, involves DNA or RNA recombination. By using altered Harvey sarcoma proviruses as models for transduction intermediates, we have investigated the mechanism of regeneration of transforming virus from truncated proviruses with only a single 5' long terminal repeat (LTR) but with a complete 5'-LTR-ras transforming gene. The Harvey proviruses were specifically altered to discriminate between virus regeneration by RNA template switching during reverse transcription, as has been postulated, and virus regeneration by DNA recombination with either helper virus or among elements of the defective provirus alone. For this purpose U3 elements of the Harvey proviral LTR, which are essential for replication but not for transcription, were deleted in vitro. Only proviral constructions with an intact or a nearly intact single LTR regenerated infectious Harvey sarcoma virus. Since all constructions transformed cells and produced identical RNAs, our results exclude a model of virus regeneration by switching of RNA templates during reverse transcription. We conclude that regeneration of infectious Harvey viruses from truncated provirus involved illegitimate recombination of cellular or cotransfected DNAs flanking the 5'-LTR-ras gene of Harvey sarcoma virus. Based on this and evidence from the literature, we propose that retroviral transduction proceeds by way of rare illegitimate recombinations between proviral and cellular DNAs.

myc protooncogene linked to retroviral promoter, but not to enhancer, transforms embryo cells

To define conditions under which the chicken protooncogene p-myc is converted to a viral and possibly to a cellular transforming gene, we assayed transforming function of hybrid genes put together from cloned retroviral and p-myc elements and of p-myc genes isolated from spontaneous viral lymphomas. Transforming function was measured in quail embryo cells transfected with cloned myc genes. We found that only myc genes with a promoter of a retroviral long terminal repeat (LTR) located between the native p-myc promoter and the second p-myc exon have transforming function. Transforming efficiencies decreased with increasing lengths of unspliced sequences between the LTR and p-myc exon 2. p-myc DNAs with LTRs downstream of the coding region or upstream but in the opposite transcriptional orientation failed to transform embryo cells. Likewise, only those retroviral-p-myc combinations from chicken B-cell lymphomas with a LTR positioned as promoter upstream of p-myc exon 2 had transforming function. We conclude that substitution of a retroviral LTR for the promoter and for as yet poorly defined, untranscribed regulatory elements of p-myc is sufficient to convert chicken p-myc to a transforming gene. However, retroviral LTRs can only convert p-myc genes to embryo-cell-transforming genes from a limited number of positions, and not as position-independent enhancers. Further, we deduce that there are two classes of viral chicken B-cell lymphomas, those with and those without embryo-cell-transforming p-myc genes.

Cancer genes generated by rare chromosomal rearrangements rather than activation of oncogenes

The 20 known transforming onc genes of retroviruses are defined by sequences that are transduced from cellular genes, termed proto-oncogenes or cellular oncogenes. Based on these sequences, viral onc genes have been postulated to be transduced cellular cancer genes and proto-onc genes have been postulated to be latent cancer genes that can be activated from within the cell to cause virus-negative tumors. The hypothesis is popular because it promises direct access to cellular cancer genes. However, the existence of latent cancer genes presents a paradox since such genes are clearly undesirable. The hypothesis predicts (i) that viral onc genes and proto-onc genes are isogenic, (ii) that expression of proto-onc genes induces tumors, (iii) that activated proto-onc genes transform diploid cells upon transfection, like viral onc genes, and (iv) that diploid tumors exist that differ from normal cells only in transcriptionally or mutationally activated proto-onc genes. As yet, none of these predictions is confirmed. Moreover, the probability of spontaneous transformation in vivo is at least 10(9) times lower than predicted from the mechanisms thought to activate proto-onc genes. Therefore the hypothesis, that proto-onc genes are latent cellular oncogenes, appears to be an overinterpretation of sequence homology to structural and functional homology with viral onc genes. Here it is proposed that only rare truncations and illegitimate recombinations that alter the germline configuration of cellular genes, generate viral and possibly cellular cancer genes. The clonal chromosome abnormalities that are consistently found in tumor cells are microscopic evidence for rearrangements that may generate cancer genes. The clonality indicates that the tumors are initiated with, and possibly by, these abnormalities as predicted by Boveri in 1914 (Zur Frage der Entstehung maligner Tumoren, Jena, Fischer).

Cancer genes: rare recombinants instead of activated oncogenes (a review)

The 20 known transforming (onc) genes of retroviruses are defined by sequences that are transduced from cellular genes termed protooncogenes or cellular oncogenes. Based on these sequences, viral onc genes have been postulated to be transduced cellular cancer genes, and proto-onc genes have been postulated to be latent cancer genes that can be activated from within the cell to cause virus-negative tumors. The hypothesis is popular because it promises direct access to cellular cancer genes. However, the existence of latent cancer genes presents a paradox, since such genes are clearly undesirable. The hypothesis predicts that viral onc genes and proto-onc genes are isogenic; that expression of proto-onc genes induces tumors; that activated proto-onc genes transform diploid cells upon transfection, like viral onc genes; and that diploid tumors exist. As yet, none of these predictions is confirmed. Instead: Structural comparisons between viral onc genes, essential retroviral genes, and proto-onc genes show that all viral onc genes are indeed new genes, rather than transduced cellular cancer genes. They are recombinants put together from truncated viral and truncated proto-onc genes. Proto-onc genes are frequently expressed in normal cells. To date, not one activated proto-onc gene has been isolated that transforms diploid cells. Above all, no diploid tumors with activated proto-onc genes have been found. Moreover, the probability of spontaneous transformation in vivo is at least 10(9) times lower than predicted from the mechanisms thought to activate proto-onc genes. Therefore, the hypothesis that proto-onc genes are latent cellular oncogenes appears to be an overinterpretation of sequence homology to structural and functional homology with viral onc genes. Here it is proposed that only rare truncations and illegitimate recombinations that alter the germ-line configuration of cellular genes generate viral and possibly cellular cancer genes. The clonal chromosome abnormalities that are consistently found in tumor cells are microscopic evidence for rearrangements that may generate cancer genes. The clonality indicates that the tumors are initiated with, and possibly by, these abnormalities, as predicted by Boveri in 1914.

Retroviruses as carcinogens and pathogens: expectations and reality

Retroviruses (without transforming genes) are thought to cause leukemias and other cancers in animals and humans because they were originally isolated from those diseases and because experimental infections of newborns may induce leukemias with probabilities of 0 to 90%. According to this hypothesis viral cancers should be contagious, polyclonal, and preventable by immunization. However, retroviruses are rather widespread in healthy animals and humans where they typically cause latent infections and antiviral immunity. The leukemia risk of such infections is less than 0.1% and thus about as low as that of virus-free controls. Indeed retroviruses are not sufficient to initiate transformation because of the low percentage of symptomatic virus carriers and the complete lack of transforming function in vitro; because of the striking discrepancies between the long latent periods of 0.5 to 10 years for carcinogenesis and the short eclipse of days to weeks for virus replication and direct pathogenic and immunogenic effects; because there is no gene with a late transforming function, since all genes are essential for replication; because host genes, which do not inhibit virus, inhibit tumorigenesis up to 100% if intact and determine the nature of the tumor if defective; and above all because of the monoclonal origin of viral leukemias, defined by viral integration sites that are different in each tumor. On these bases the probability that a virus-infected cell will become transformed is estimated to be about 10(-11). The viruses are also not necessary to maintain transformation, since many animal and all bovine and human tumors do not express viral antigens or RNA or contain only incomplete proviruses. Thus as carcinogens retroviruses do not necessarily fulfill Koch's first postulate and do not or only very rarely (10(-11)) fulfill the third. Therefore it has been proposed that retroviruses transform inefficiently by activating latent cellular oncogenes by for example provirus integration. This predicts diploid tumors with great diversity, because integration sites are different in each tumor. However, the uniformity of different viral and even nonviral tumors of the same lineage, their common susceptibility to the same tumor resistance genes, and transformation-specific chromosome abnormalities shared with non-viral tumors each argue for cellular transforming genes. Indeed clonal chromosome abnormalities are the only known transformation-specific determinants of viral tumors. Since tumors originate with these abnormalities, these or associated events, rather than preexisting viruses, must initiate transformation.(ABSTRACT TRUNCATED AT 250 WORDS)

Latent cellular oncogenes: the paradox dissolves

The 20 known transforming onc genes of retroviruses are defined by sequences which are transduced from cellular genes, termed proto-onc genes. Based on these sequences, viral onc genes have been postulated to be transduced cellular cancer genes and proto-onc genes have been postulated to be latent cancer genes that can be activated from within the cell, to cause virus-negative tumours. The hypothesis is popular because it promises direct access to cellular cancer genes. However the existence of latent cancer genes presents a paradox since such genes would be most undesirable for eukaryotes. The hypothesis predicts (i) that viral onc genes and proto-onc genes are isogenic, (ii) that expression of proto-onc genes induces tumours, (iii) that activated proto-onc genes transform diploid cells upon transfection, like viral onc genes, and (iv) it predicts diploid tumours. As yet, none of these predictions is confirmed. Instead: (i) Structural comparisons between viral onc genes, essential retroviral genes, and the proto-onc genes show that all viral onc genes are indeed new genes, rather than transduced cellular cancer genes. They are genetic hybrids put together from truncated viral and truncated proto-onc genes. (ii) Proto-onc genes are frequently expressed in normal cells. (iii) To date, not one activated proto-onc gene has been isolated that transforms diploid cells. (iv) Above all, no diploid tumours with activated proto-onc genes have been found. Moreover the probability of spontaneous transformation in vivo is at least 10(9) times lower than predicted from the mechanisms thought to activate proto-onc genes. Therefore the hypothesis, that proto-onc genes are latent cellular oncogenes, appears to be an over-interpretation of sequence homology to structural and functional homology with viral onc genes. Here is is proposed that only rare truncations and recombinations, that alter the germline configuration of cellular genes, generate viral and possibly cellular cancer genes. The clonal chromosome abnormalities that are consistently found in tumour cells are microscopic evidence for rearrangements that may generate cancer genes. The clonality indicates that the tumours are initiated with, and possibly by these abnormalities as predicted by Boveri in 1914.

Harvey ras genes transform without mutant codons, apparently activated by truncation of a 5' exon (exon -1)

The hypothesis is tested that the ras gene of Harvey sarcoma virus (Ha-SV) and the proto-ras DNAs from certain tumor cells derive transforming function from specific codons in which they differ from normal proto-ras genes. Molecularly cloned Harvey proviral vectors carrying viral ras, normal rat proto-ras, and recombinant ras genes in which the virus-specific ras codons 12 and 59 were replaced by proto-ras equivalents each transformed aneuploid mouse 3T3 cells after latent periods that ranged from 4 to 10 days. Viruses with or without virus-specific ras codons all transformed diploid rat cells in 3-5 days equally well. However, in the absence of virus replication, mutant codons were beneficial for transforming function. Deletion of non-ras regions of Ha-SV did not affect transforming function. We conclude that specific ras codons are not necessary for transforming function. Comparisons of the ras sequences of Ha-SV, BALB SV, and Rasheed SV with sequences of proto-ras genes from rat and man revealed an upstream proto-ras exon, termed exon -1. The 3' end of this exon is present in all three viruses and in a ras pseudogene of the rat. Since ras genes transform without mutation and since exon -1 is truncated in viral ras genes and all transforming proto-ras DNAs of the Harvey and the Kirsten ras family, we propose that ras genes are activated by truncation of exon -1 either via viral transduction or artificially via cloning and transfection. The proposal implies that untruncated proto-ras genes with point mutations may not be cellular cancer genes.

The ets sequence from the transforming gene of avian erythroblastosis virus, E26, has unique domains on human chromosomes 11 and 21: both loci are transcriptionally active

Human DNA segments homologous to the ets region from the transforming gene of avian erythroblastosis virus, E26, were molecularly cloned and shown to be closely related to the viral equivalent by hybridization and partial sequence analysis. The transforming gene of E26 has a tripartite origin with the structure delta gag [1.2 kilobases (kb) from the viral gag gene]-myb(0.9 kb from the chicken myb gene)-ets (1.6 kb from the chicken ets gene). Human ets DNA is located on two distinct human chromosomes. The human ets-1 locus on chromosome 11 encodes a single mRNA of 6.8 kb; the second locus, ets-2 on chromosome 21, encodes three mRNAs of 4.7, 3.2, and 2.7 kb. The ets-related sequences of human DNA on chromosomes 11 and 21 are discontiguous, except for a small overlap region encoding 14 amino acids, where 12 are conserved between these two loci. By contrast, the chicken homolog has contiguous ets-1 and ets-2 sequences and is primarily expressed in normal chicken cells as a single 7.5-kb mRNA. We conclude that the ets sequence shared by the virus, the chicken, and humans is likely to contain at least two dissociable functional domains, ets-1 and ets-2. Thus, the tripartite transforming gene of E26 includes four distinct domains that may be functionally relevant for the transforming function of the virus (delta gag, myb, ets-1, and ets-2).

Defining the borders of the chicken proto-fps gene, a precursor of Fujinami sarcoma virus

The transforming (onc) genes of retroviruses contain specific sequences, derived from as yet poorly defined, normal cellular genes, termed proto-onc genes. Proto-onc genes must be defined to explain their docility compared to the oncogenicity of the viral derivatives. Here we set out to determine the borders of the chicken proto-fps gene from which the onc genes of avian Fujinami (FSV) and PRC sarcoma viruses (PRCSV) are derived. These onc genes are hybrids of an element from the gag gene of retroviruses (delta gag) linked to a 2.8-kb domain from proto-fps. To identify the 5' border of proto-fps we have sequenced 1.5 kb beyond the 5' border of overlap with viral fps utilizing a proto-fps clone derived previously. A possible promoter was identified that maps 736 nucleotides from this border. The 736 nucleotides contain two possible exons with 121 codons, and short regions of homology with the delta gag termini of FSV and PRCII. A translation stop codon and an adjacent polyadenylation signal were identified just prior to the 3' border of overlap with viral fps within a 1.15-kb sequence of a newly isolated proto-fps clone. Comparing four exons within this 1.15 kb proto-fps sequence with known fps equivalents of FSV and PRCSV, we have detected strain-specific, but no common point mutations in each viral genome. A 3.3-kb polyadenylated proto-fps mRNA was detected in chicken liver RNA by gel electrophoresis and hybridization with proto-fps DNA. We conclude that the coding capacity of proto-fps is just over 3 kb, consistent with the size of the putative proto-fps protein of 98 kDa and hence slightly larger than that of viral fps. Thus proto-fps and the viral delta gag-fps genes each contain distinct 5' regulatory and coding sequences and share the 3' terminal fps domains. It is suggested that this difference, rather than scattered point mutations, is responsible for the oncogenic function of the viral genes and the unknown cellular function of proto-fps.

Activated proto-onc genes: sufficient or necessary for cancer?

Proto-onc genes are normal cellular genes that are related to the transforming (onc) genes of retroviruses. Because of this relationship these genes are now widely believed to be potential cancer genes. In some tumors, proto-onc genes are mutated or expressed more than in normal cells. Under these conditions, proto-onc genes are hypothesized to be active cancer genes in one of two possible ways: The one gene-one cancer hypothesis suggests that one activated proto-onc gene is sufficient to cause cancer. The multigene-one cancer hypothesis suggests that an activated proto-onc gene is a necessary but not a sufficient cause of cancer. However, mutated or transcriptionally activated proto-onc genes are not consistently associated with the tumors in which they are occasionally found and do not transform primary cells. Further, no set of an activated proto-onc gene and a complementary cancer gene with transforming function has yet been isolated from a tumor. Thus, there is still no proof that activated proto-onc genes are sufficient or even necessary to cause cancer.

Two oncogenes in avian carcinoma virus MH2: myc and mht

The 5.2-kilobase (kb) RNA genome of avian carcinoma virus MH2 has the genetic structure 5' - delta gag (0.2 kb)-mht (1.2 kb)-myc (1.4 kb)-c(0.4 kb)-poly (A) (0.2 kb)-3'. delta gag is a partial retroviral core protein, mht and myc are cell-derived MH2-specific sequences, and c is the 3'-terminal retroviral vector sequence. the following results were obtained from the complete nucleotide sequences of the mht and myc genes in MH2. (i) delta gag-mht forms a hybrid gene with a contiguous reading frame of 2682 nucleotides that terminates with a stop codon near the 3' end of the mht gene. The 3' 969 nucleotides of mht up to the stop codon are 80% sequence related to the onc-specific raf sequence of murine sarcoma virus 3611 (MSV 3611) (94% homologous at the deduced amino acid level). (ii) The myc coding region in MH2 is preceded by 181 nucleotides derived from the intron immediately upstream from the second exon of the chicken cellular proto-myc gene, followed by an RNA splice acceptor site shared with the proto-myc gene, followed by an RNA splice acceptor site shared with the proto-myc, beyond which it is colinear up to a 3'-termination codon and 40 noncoding nucleotides with the myc sequences of avian retrovirus MC29 and chicken proto-myc. Thus, myc forms, together with a 5' retroviral exon, a second MH2-specific gene. It is concluded that MH2 contains two genes with oncogenic potential, the delta gag-mht gene, which is closely related to the delta gag-raf transforming gene of MSV 3611, and the myc gene, which is related to the transforming gene of MC29. Furthermore, it may be concluded that the cellular proto-onc genes, which on sequence transduction become viral onc genes, are a small group because among the 19 known onc sequences, 5 are shared by different taxonomic groups of viruses of which the mht/raf homology is the closest so far.

A relationship between the yeast cell cycle genes CDC4 and CDC36 and the ets sequence of oncogenic virus E26

We report here significant primary sequence homology among the predicted translational products of three genes: CDC4 , CDC36 and ets. CDC4 and CDC36 are Saccharomyces cerevisiae cell division cycle genes, while ets is a transformation-specific sequence of avian erythroblastosis virus E26. The deduced primary structures of the three gene products were compared by computer to a large data base of known and predicted protein sequences. The search revealed 22.0-25.5% identity over regions of 140-206 codons, respectively between the different pairwise combinations. For these particular sequences, these identity scores fall 3.4-4.0 standard deviations above the empirically-determined mean values of fortuitous similarity. S. cerevisiae calls require CDC36 and CDC4 in order to complete two early events in the cell cycle: execution of start ( CDC36 ) and spindle pole body separation ( CDC4 ). In virus E26, the ets sequence is linked in frame with delta gag and mybE in the tripartite structure 5'-delta gag- mybE -ets-3', comprising the E26 transforming oncogene. The homologies described here suggest that the biochemical functions or regulation of the CDC4 , CDC36 and ets products may be related.

Nucleotide sequence of avian carcinoma virus MH2: two potential onc genes, one related to avian virus MC29 and the other related to murine sarcoma virus 3611

The 5.2-kilobase (kb) RNA genome of avian carcinoma virus MH2 has the genetic structure 5'-delta gag (0.2 kb)- mht (1.2 kb)-myc (1.4 kb)-c (0.4 kb)-poly(A) (0.2 kb)-3'. delta gag is a partial retroviral core protein gene, mht and myc are cell-derived MH2-specific sequences, and c is the 3'-terminal retroviral vector sequence. Here we have determined the nucleotide sequence of 3.5 kb from the 3' end of delta gag to the 3' end of molecularly cloned proviral MH2 DNA, in order to elucidate the genetic structure of the virus and to compare it with other mht - and myc-containing oncogenic viruses as well as with the chicken proto-myc gene. The following results were obtained: (i) delta gag- mht forms a hybrid gene with a contiguous reading frame of 2682 nucleotides that terminates with a stop codon near the 3' end of mht . The 3' 969 nucleotides of mht up to the stop codon are 80% sequence related to the onc-specific raf sequence of murine sarcoma virus 3611 (94% homologous at the deduced amino acid level). (ii) The myc sequence is preceded by an RNA splice acceptor site shared with the cellular proto-myc gene, beyond which it is colinear up to a 3'-termination codon and 40 noncoding nucleotides with the myc sequences of avian retrovirus MC29 and chicken proto-myc. Thus, myc forms, together with a 5' retroviral exon, a second MH2-specific gene. (iii) myc is followed by the 3'-terminal c region of about 400 nucleotides, which is colinear with that of Rous sarcoma virus except for a substitution near the 5' end of the long terminal repeat. It is concluded that MH2 contains two genes with oncogenic potential, the delta gag- mht gene, which is closely related to the delta gag-raf transforming gene of MSV 3611, and the myc gene, which is related to the transforming gene of MC29. Furthermore, it may be concluded that the cellular proto-onc genes, which on sequence transduction become viral onc genes, are a small group because among the 19 known onc sequences, 5 are shared by different taxonomic groups of viruses of which the mht /raf homology is the closest determined so far.

Complete env gene deletions of three replication-defective strains of Rous sarcoma virus and a model for the origin of their genetic structures

Replication-defective deletion mutants of Rous sarcoma virus (RSV) have been described which transform cells in culture and elaborate envelope (-) defective particles. The env deletions of two clonal variants of the Bryan strain of RSV, RSV(-)3, and RSV(-)16, and of a replication-defective variant of Schmidt-Ruppin RSV (SRN8) were analyzed by fingerprinting oligonucleotides hybridized by a molecularly cloned env DNA probe that spans from near the 3' end of pol to the 3' end of env. It was observed that all three replication-defective RSV strains are essentially complete env deletions but retain the 3' end of pol. Based on a common pol-src junction oligonucleotide that may reflect a homologous sequence repeated at both ends of env in nondefective RSV, the env deletions of RSV(-)3 and 16 appear to be isogenic. The original deletion may have involved recombination between these sequences. The absence of this oligonucleotide in SRN8 indicates that the env deletion of SRN8 has different borders and represents an independent env deletion of nondefective RSV. All three defective RSVs have the genetic structure gag-pol-src. This genetic structure is consistent with the need for a complete gag to make a particle and with the assumption that an independent src gene rather than a gag- or gag-pol-src hybrid gene functions in transformation. It is suggested that a complete pol is not necessary for, but may assist, virus particle formation.

The 5' ends of the transforming gene of Fujinami sarcoma virus and of the cellular proto-fps gene are not colinear

The sequence of 500 nucleotides of a cellular proto-fps region that includes the 5' boundary of overlap with the fps sequence of Fujinami sarcoma virus (FSV) was determined. It was found that the potential reading frame of the proto-fps region continues over the 5' boundary of overlap with viral fps for 44 codons which do not include an AUG translation initiation codon. A potential upstream exon of proto-fps of over 91 codons and a potential splice acceptor at the site of fps/proto-fps overlap have been identified. It is concluded that the boundary of overlap between proto-fps and viral fps cannot represent the 5' end of the coding region of proto-fps. The proto-fps gene starts either in the upstream exon(s) not shared with FSV or at least 51 codons downstream of the boundary of overlap with FSV. In addition, the 5' coding region of proto-fps differs from the (delta gag-fps) hybrid transforming gene of FSV in the absence of the retroviral gag gene-derived sequence.