Translation of Rous sarcoma virus RNA in a cell-free system from ascites Krebs II cells

The pathophysiology of murine retrovirus-induced leukemias

Murine leukemia viruses (MuLVs) are retroviruses which induce a broad spectrum of hematopoietic malignancies. In contrast to the acutely transforming retroviruses, MuLVs do not contain transduced cellular genes, or oncogenes. Nonetheless, MuLVs can cause leukemias quickly (4 to 6 weeks) and efficiently (up to 100% incidence) in susceptible strains of mice. The molecular basis of MuLV-induced leukemia is not clear. However, the contribution of individual viral genes to leukemogenesis can be assayed by creating novel viruses in vitro using recombinant DNA techniques. These genetically engineered viruses are tested in vivo for their ability to cause leukemia. Leukemogenic MuLVs possess genetic sequences which are not found in nonleukemogenic viruses. These sequences control the histologic type, incidence, and latency of disease induced by individual MuL Vs.

Expansion of a minor subpopulation of peripheral blood lymphocytes (T8+/Leu 7+) in patients with haemophilia

Immunological analysis of peripheral blood mononuclear cells (PBM) was performed in 20 patients with haemophilia A or B. One of the patients had never received clotting factor substitution in his life. Six different sources of lyophilized clotting factor were used for the other patients, but every given patient received factor from one source, exclusively. None of the patients exhibited lymphadenopathy and only one suffered from local bacterial infection. Mononuclear cell counts were within the normal range and mitogen stimulation with phythaemagglutinin (PHA) and concanavalin A (Con A) was found normal in all but two patients. Ratios of helper and suppressor cells (T4/T8) were below 1.0 in 10 of the patients. Some of these patients had a relative increase of T8+ cells and at the same time of Leu 7+ (natural killer (NK)/suppressor) cells. Double-marker analysis revealed that the subpopulation of cells expressing both the T8 and the Leu 7 antigen, which on the average accounted for 2.1% of the mononuclear cells in controls, was increased 4.5 fold (9.1%) in haemophilia patients. One patient exhibited 37.8% T8+/Leu 7+ double-marker cells. VEP13+ cells (active NK cells) were decreased below the normal range in 11 of the patients. Abnormal values for lymphocyte subsets were found in every treatment group. The patient who had never received any clotting factor exhibited normal values in all respects. In an additional set of patients, those with increased percentage of T8+/Leu 7+ cells exhibited decreased NK cell activity indicating that the T8+/Leu 7+ cells are not active NK cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Complete nucleotide sequence of the AIDS virus, HTLV-III

The complete nucleotide sequence of two human T-cell leukaemia type III (HTLV-III) proviral DNAs each have four long open reading frames, the first two corresponding to the gag and pol genes. The fourth open reading frame encodes two functional polypeptides, a large precursor of the major envelope glycoprotein and a smaller protein derived from the 3'-terminus long open reading frame analogous to the long open reading frame (lor) product of HTLV-I and -II.

Presence of antibodies to human lymphoma-leukemia virus (HTLV-I) in Germans with symptoms of the acquired immunodeficiency syndrome (AIDS)

Sera from German patients exhibiting symptoms compatible with the acquired immune deficiency syndrome (AIDS) or the lymphadenopathy syndrome (LAS) were assayed for antibodies against human T-cell lymphoma/leukemia virus (HTLV-I)-related antigens by enzyme immunoassay, indirect immunofluorescence, and radioimmunoprecipitation. Antibodies against HTLV were detected in 3 out of 31 sera.

Avian sarcoma virus gag and env gene structural protein precursors contain a common amino-terminal sequence

The initiation site for translation of the avian sarcoma virus glycoprotein precursor, Pr63env, has been determined by analyzing the amino-terminal peptides of Pr63env and the polyprotein precursor Pr76gag encoded by the viral gag gene. The acceptor splice junction used to form the env gene mRNA has also been identified. Hybrid-selected virus-specific mRNAs were translated in vitro in the presence of either L-[35S]methionine to label at every methionine residue or L-[35S]methionine-tRNAMeti to label specifically at the amino-terminal methionine residues. Tryptic peptide maps of Pr63env labeled at every methionine residue contain all of the peptides, plus one additional peptide, present in the map of Pr57env, a nonglycosylated env-encoded polypeptide of molecular weight 57,000 immunoprecipitated from tunicamycin-treated cells. Specific amino-terminal labeling of the in vitro-synthesized polypeptides showed that the peptide missing from Pr57env corresponds to the amino-terminal tryptic peptide of Pr63env, which is removed in vivo as part of the amino-terminal signal peptide. Comparison of the amino-terminal tryptic peptides of Pr63env and Pr76gag showed that they are identical. In contrast, the chymotryptic amino-terminal peptides of Pr76gag and Pr63env are not identical. The location of the acceptor-splice junction in the env mRNA of the Prague A strain of avian sarcoma virus was determined by mung bean nuclease mapping to be at nucleotide 5,078. Fusion of the gag and env gene sequences during splicing results in use of the same AUG codon to initiate synthesis of Pr76gag and Pr63env. This sequence is contained within the 397-nucleotide 5' terminal leader that is spliced to the body of the env mRNA. The possible significance of these results for the regulation of avian sarcoma virus synthesis and translation is discussed.

In vitro synthesis of M and Z forms of human alpha 1-antitrypsin

mRNA was prepared from autopsy liver samples from a homozygote for alpha 1-antitrypsin deficiency (PiZZ) and from a normal (PiMM) subject. Both preparations gave equivalent synthesis of alpha 1-antitrypsin in a wheat germ cell-free system. This suggests that the deficiency of plasma alpha 1-antitrypsin associated with the Z variant is due to a failure of processing and secretion of the protein rather than of its synthesis. It is likely that it is the resultant intracellular accumulation of the Z protein rather than a deficiency of protease inhibitor that is the primary cause of the liver pathology associated with this variant.

Accumulation of spliced avian retrovirus mRNA is inhibited in S-adenosylmethionine-depleted chicken embryo fibroblasts

The synthesis and processing of B77 avian sarcoma virus RNA in infected chicken embryo fibroblasts was followed in the presence and absence of cycloleucine, a competitive inhibitor of the synthesis of S-adenosylmethionine and thus an inhibitor of RNA methylations. An increase in the steady-state levels of genome-length RNA and a decrease in the steady-state levels of subgenomic RNA molecules were obtained in the S-adenosylmethionine-depleted avian sarcoma virus-infected cells after 24 h of treatment with the inhibitor. The total number of virus-specific RNA molecules per cell, however, remained relatively constant under either condition. The production of newly synthesized virus-specific RNA in cycloleucine-treated and untreated cells infected with a transformation-defective strain of B77 avian sarcoma virus was followed as a function of [(3)H]uridine labeling time. The accumulation of radioactive genome-length 8.4-kilobase (kb) RNA continued in cycloleucine-treated cells, and virus particle production proceeded at normal rates as previously shown by incorporation of labeled nucleoside precursors or amino acids. In contrast, newly synthesized 3.5-kb subgenomic mRNA, the putative mRNA for the envelope protein precursor, failed to accumulate in the treated cells. The extent of the inhibition in the appearance of the radioactive 3.5-kb RNA was correlated with the extent of the inhibition of viral genomic and cellular mRNA methylations and was a function of the cycloleucine concentration. Under conditions in which the accumulation of 3.5-kb envelope protein mRNA was blocked by the cycloleucine treatment, there were significant increases in the rate of synthesis of the polypeptide products of the genome-length RNA, the precursors to the non-glycosylated gag proteins (Pr76(gag)), and the reverse transcriptase (Pr 180(gag pol)) relative to the rate of synthesis of the envelope protein precursor (gPr 92(env)). These results suggest that there is an S-adenosylmethionine requirement for the splicing, but not for the synthesis, packaging, or messenger function, of avian retrovirus genome-length RNA. Possible reasons for this requirement are discussed.

The leader sequence of the subgenomic mRNA's of Rous sarcoma virus is approximately 390 nucleotides

The subgenomic mRNA's of Rous sarcoma virus share a common 5' leader sequence spliced from genomic RNA. We have examined the 5' terminal sequences of four Rous sarcoma virus RNAs: virion RNA and three species of intracellular mRNA which direct the synthesis of the RSV gene products. The lengths of the leaders on the RNAs were determined by the extent that they could protect cloned Rous sarcoma virus DNA fragments from S1 nuclease digestion after RNA-DNA hybridization. We found that the subgenomic mRNA's that direct the synthesis of the env and src gene products have uninterrupted spliced leader sequences of approximately 390 nucleotides, whereas virion RNA and full-length intracellular viral RNA have 5' termini homologous to the cloned viral DNA probe over at least the first 735 bases. In the accompanying manuscript we have determined the nucleotide sequence of the 5' end of the Rous sarcoma virus genome, including the candidate splice donor site identified here (Swanstrom et al., J. Virol. 41:535-541, 1982).

Nucleotide sequence of the 5' noncoding region and part of the gag gene of Rous sarcoma virus

Several functions of the retrovirus genome involve structural features in the vicinity of its 5' terminus. In an effort to further elucidate the relationship between structure and function in retrovirus RNA, we have determined the sequence of the first 1,010 nucleotides at the 5' end of the genome of Rous sarcoma virus by using the Maxam-Gilbert method to sequence suitable domains in cloned Rous sarcoma virus DNA. The results (i) locate the initiation codon for the gag gene of Rous sarcoma virus 372 nucleotides from the 5' end of viral RNA; (ii) demonstrate that this codon is preceded by three methionine codons that are apparently not used in translation; (iii) sustain previous conclusions that the principal site to which ribosomes bind on the Rous sarcoma virus genome in vitro does not contain the initiation codon for gag; (iv) permit deduction of the amino acid sequence of a viral structural protein, p19; (v) confirm the amino-terminal sequence of Pr76gag; and (vi) substantiate the identification of a splice donor site described in the accompanying manuscript (Hackett et al., J. Virol., 41:527-534, 1982).

Genome structure of avian sarcoma virus Y73 and unique sequence coding for polyprotein p90

The genome structure of a newly isolated sarcoma virus, Y73, was studied. Y73 is a defective, potent sarcomagenic virus and contains 4.8-kilobase (kb) RNA as its genome; in contrast, helper virus associated with Y73 had 8.5-kb RNA, similar to other avian leukemia viruses. Fingerprinting analysis these RNAs demonstrated that the 4.8-kb RNA contains a specific RNA sequence of 2.5 kb, which represents the transforming gene (yas) of Y73. This specific sequence was mapped in the middle of the genome and had at both ends 1- to 1.5-kb sequences in common with Y73-associated virus RNA. This structure is very similar to those of avian and mammalian leukemia viruses. In vitro translation of the 4.8-kb RNA and the immunospecificity of the products directly demonstrated that polyprotein p90, containing p19, is a product translated from capped 4.8-kb RNA and that the specific peptide portion is coded by the yas sequence. Protein 90, which was also found in cells transformed with Y73, was suggested to be a transforming protein.

Avian erythroblastosis virus produces two mRNA's

We analyzed the viral mRNA's present in fibroblast nonproducer clones transformed by avian erythroblastosis virus. Two size classes of mRNA (28 to 30S and 22 to 24S) were identified by solution hybridization with both complementary DNA strong stop and complementary DNA made against the unique sequences of avian erythroblastosis virus. Based upon the kinetics of hybridization with complementary DNA made against the unique sequences of avian erythroblastosis virus, we estimated that there were 400 to 500 copies of the 28 to 30S RNA per cell and 200 to 250 copies of the 22 to 24S RNA per cell. Both RNA species were packaged in the virion. In vitro translation of the 28 to 30S virion RNA yielded a 75,000-dalton protein which was the 75,000-dalton gag-related polyprotein found in avian erythroblastosis virus-transformed cells. In vitro translation of the 22 to 24S virion RNA yielded two proteins (46,000 and 48,000 daltons). This indicates that there may be two genes in avian erythroblastosis virus, one coding for the 75,000-dalton gag-related polyprotein and the second coding for the 46,000- or 48,000-dalton protein or both.

Genetic variation and host markers in the src gene of recovered avian sarcoma viruses

The src genes of three recovered avian sarcoma viruses were compared by RNase T1 oligonucleotide fingerprinting and tryptic peptide analysis. In all three recovered avian sarcoma viruses the oligonucleotide composition of src was different and also distinct from that of the parental Schmidt-Ruppin strain of Rous sarcoma virus. This evidence for genetic variation src was strengthened by two dimensional peptide maps of the src gene products pp60src, translated in a reticulocyte lysate system in vitro. Numerous differences between the peptide patterns of the pp60src proteins produced by the parental and the recovered viruses were detected. No two src proteins were identical, while the tryptic peptide maps of the internal gag proteins synthesized by these viruses were indistinguishable. The src proteins of recovered avian sarcoma viruses also contained peptides that were absent from the src protein of parental Schmidt-Ruppin D virus but were found in the endogenous src protein of normal cells. We conclude that there is considerable genetic variation in the src gene of recovered avian sarcoma viruses and that these recovered src genes contain host cell-derived markers.

Sites of synthesis of viral proteins in avian sarcoma virus-infected chicken cells

We determined the sites of synthesis of avian sarcoma virus-specific proteins in infected chicken cells by immunoprecipitation of the products synthesized in vitro by free and membrane-bound polyribosomes; 85% of Pr76, the precursor of the viral internal structural proteins (group-specific antigens), was synthesized on free polyribosomes, and 15% was synthesized on membrane-bound polyribosomes. Pr92, the lycosylated precursor of the viral glycoproteins (gp85 and gp35), was synthesized exclusively on membrane-bound polyribomes, which is consistent with its role as a membrane protein. When we investigated the site of synthesis of pp60src, the product of the avian sarcoma virus src gene, we found that 90% was synthesized on free polyribosomes, whereas 10% was detected on membrane-bound polyribosomes. The implications of these results with respect to the subcellular location of pp60src are discussed.

Suppression of murine retrovirus polypeptide termination: effect of amber suppressor tRNA on the cell-free translation of Rauscher murine leukemia virus, Moloney murine leukemia virus, and Moloney murine sarcoma virus 124 RNA

The effect of suppressor tRNA's on the cell-free translation of several leukemia and sarcoma virus RNAs was examined. Yeast amber suppressor tRNA (amber tRNA) enhanced the synthesis of the Rauscher murine leukemia virus and clone 1 Moloney murine leukemia virus Pr200(gag-pol) polypeptides by 10- to 45-fold, but at the same time depressed the synthesis of Rauscher murine leukemia virus Pr65(gag) and Moloney murine leukemia virus Pr63(gag). Under suppressor-minus conditions, Moloney murine leukemia virus Pr70(gag) was present as a closely spaced doublet. Amber tRNA stimulated the synthesis of the "upper" Moloney murine leukemia virus Pr70(gag) polypeptide. Yeast ochre suppressor tRNA appeared to be ineffective. Quantitative analyses of the kinetics of viral precursor polypeptide accumulation in the presence of amber tRNA showed that during linear protein synthesis, the increase in accumulated Moloney murine leukemia virus Pr200(gag-pol) coincided closely with the molar loss of Pr63(gag). Enhancement of Pr200(gag-pol) and Pr70(gag) by amber tRNA persisted in the presence of pactamycin, a drug which blocks the initiation of protein synthesis, thus arguing for the addition of amino acids to the C terminus of Pr63(gag) as the mechanism behind the amber tRNA effect. Moloney murine sarcoma virus 124 30S RNA was translated into four major polypeptides, Pr63(gag), P42, P38, and P23. In the presence of amber tRNA, a new polypeptide, Pr67(gag), appeared, whereas Pr63(gag) synthesis was decreased. Quantitative estimates indicated that for every 1 mol of Pr67(gag) which appeared, 1 mol of Pr63(gag) was lost.

Tryptic peptide analysis of avian oncovirus gag and pol gene products

Radiolabeled tryptic peptides of the gag and pol gene products of avian oncoviruses were examined. This analysis included Rous-associated virus 2 structural proteins and the Pr76gag and P180gag-pol proteins in Rous-associated virus 2-infected chicken embryo cells. The methionine- and cysteine-containing tryptic peptides of virion internal structural proteins were present in both Pr76gag and P180gag-pol, suggesting that there was no loss of gag gene-coding sequences during the generation of P180gag-pol. No overlap of gag and pol gene structural information was detected. Analysis of intermediates in the processing of Pr76gag and translation inhibition mapping with pactamycin yielded the following order of structural proteins within the Rous-associated virus 2 Pr76gag precursor: NH2-p19-p12-p27-p15-COOH. The gag and pol sequences missing in the endogenous gsmp120 protein of uninfected gs+ chicken cells were identified by comparison with those of Rous-associated virus 2 P180gag-pol.

Characterization of the proteins of intracisternal type A and extracellular oncornavirus-like particles produced by MOPC-460 myeloma cells

The mouse plasmacytoma cell line, MOPC-460, produces both intracisternal and intracytoplasmic A-type particles when grown as a solid tumor. When these cells are grown either as an ascites tumor or in tissue culture, a third type of particle is produced extracellularly. This particle, the "myeloma-associated virus," is closely related to, and probably an alternate form of, the intracisternal A-type particle. The proteins present in these two types of particles were compared by tryptic peptide mapping. Both types of particles were found to contain essentially the same major proteins of 76,000 (p76), 68,000 to 70,000 (p68-70), and 45,000 (p45) daltons, in addition to varying amounts of smaller proteins. The relative proportions of all these proteins varied from preparation to preparation in an unpredictable way. The p45, p68, and p70 proteins all contained sequences found in p76, suggesting precursor-product relationships of p76 leads to p70 leads to p45 for solid tumor A-type particles and p76 leads to p68 leads to p45 for extracellular myeloma-associated virus. In addition, immune precipitation experiments have established that p76 contains at least some of the antigenic determinants characteristic of murine leukemia virus p30. This confirms earlier nucleic acid hybridization studies which indicated a moderate degree of relatedness between MOPC-460 A-type particles and several standard murine leukemia and sarcoma viruses. Taken together, our results provide evidence supporting the concept that MOPC-460 A-type particles may represent aberrant forms of C-type murine viruses.

On pre-messenger RNA and transcriptions. A review

From the present review integrating old and new data emerge a few principles of gene expression in eukaryotes, and an infinite variety of possible mechanistic details generating the overal pattern. The few principles, most of which are not fundamentally new, may thus be summarized. 1) The eukaryotic genome is subdivided into transcriptional units: into transcriptons which are subject to individual activation controlled at DNA level. 2) Viral genomes may contain one or a few transcriptons, while cells of multicellular organisms contain from 3 x 10(3) in diptera up to an estimated 2 x 10(5) in birds and mammals. 3) Transcriptons may include one or several coding sequences. 4) Transcriptons vary considerably in size: in mammals and birds their size spectrum falls into the 2,000 to 20,000 bp range. 5) Units of coding information constituting one message (genes) and, possibly, units of regulative information are frequently broken up and stored within the transcripton in sub-genic blocks (of so far unknown significance) in general located at a certain distance from the 5' and 3' transcript terminals which are determined by the promotor and terminator signals. 6) The gene, in its specific definition as the functional unit underlying the phenotype, is in general constituted posttranscriptionally by the processing mechanisms from the mosaic of its genomic subunits in the transcripton; segments of coding, service and regulative sequences are recombined within themselves and with each other, polygenic transcripts separate into their unit messages. 7) Activated transcriptons produce pre-mRNA; these primary transcripts are colinear with the DNA of the transcriptional unit. 8) Primary pre-mRNA is processed into secondary pre-mRNA's by extragenic cleavage and intragenic ("splicing") processing, giving rise stepwise to functional mRNA. During this process chemical modifications as methylation, 5'-terminal capping and 3'-terminal polyadenylation take place. 9) Translation yields either potentially functional polypeptides or polycistronic polyproteins subject to further processing. 10) Processing is a regulated process; it involves many of the possible phases and mechanisms of post-transcriptional regulation (cf. 39, 40).

Cell-free synthesis of mouse mammary tumor virus Pr77 from virion and intracellular mRNA

Mouse mammary tumor virus (MuMTV) was purified from two cell lines (GR and Mm5MT/c1), and the genomic RNA was isolated and translated in vitro in cell-free systems derived from mouse L cells and rabbit reticulocytes. The major translation product in both systems was a protein with the molecular weight 77,000. Several other products were also detected, among them a 110,000-dalton and in minor amounts a 160,000-dalton protein. All three polypeptides were specifically immunoprecipitated by antiserum raised against the major core protein of MuMTV (p27), but they were not precipitated by antiserum against the virion glycoprotein gp52. Analysis of the in vitro products by tryptic peptide mapping established their relationship to the virion non-glycosylated structural proteins. The 77,000-dalton polypeptide was found to be similar, if not identical, to an analogous precursor isolated from MuMTV-producing cells. Peptide mapping of the 110,000-dalton protein shows that it contains all of the methionine-labeled peptides found in the 77,000-dalton protein plus some additional peptides. We conclude that the products synthesized in vitro from the genomic MuMTV RNA are related to the non-glycosylated virion structural proteins. Polyadenylic acid-containing RNA from MuMTV-producing cells also directed the synthesis of the 77,000-dalton polypeptide in the L-cell system. If this RNA preparation was first fractionated by sucrose gradient centrifugation the 77,000-dalton protein appeared to be synthesized from mRNA with a sedimentation coefficient between 25 and 35S.

Messenger activity of virion RNA for avian leukosis viral envelope glycoprotein

An intracellular assay for viral envelope glycoprotein (env) messenger was employed to analyze the RNA from virus particles of Rous-associated virus type 2. For this assay RNA was microinjected into cells infected by the env-deficient Bryan strain of Rous sarcoma virus [RSV(-) cells]. Only when the injected RNA could be translated by the recipient cells to produce viral envelope glycoprotein was the env deficiency of the RSV(-) cells complemented, enabling them to release focus-forming virus. RNA in a 21S size fraction from the Rous-associated virus particle promoted the release of numerous focus-forming virus from RSV(-) cells, whereas the major 35S virion RNA species was inactive. The env messenger activity sedimented as a sharp peak with high specific activity. RNase T1-generated fragments of virion 35S RNA were unable to promote the release of infectious virus from RSV(-) cells. Consequently, the active molecule was most likely to be env messenger which had been encapsulated by the virus particle from the cytoplasm of infected cells. Approximately 95% of the env messenger within the virion was associated with the virion high-molecular-weight RNA complex. The temperature required to dissociate env messenger from the high-molecular-weight complex was indistinguishable from the temperature required to disrupt the complex itself. Virion high-molecular-weight RNA that was associated with env messenger sedimented slightly more rapidly than the bulk virion RNA; this was the strongest evidence that the 21S messenger had been encapsulated directly from the infected cells. These data are considered along with a related observation [concerning the prolonged expression of env messenger after injection into RSV(-) cells] to raise the possibility that virus-encapsulated env messenger can become expressed within subsequently infected cells.

Anatomy of the RNA and gene products of MC29 and MH2, two defective avian tumor viruses causing acute leukemia and carcinoma: evidence for a new class of transforming genes

The RNA species of the defective avian acute leukemia virus MC29 and of the defective avian carcinoma virus MH2 and of their helper viruses were analyzed using gel electrophoresis, fingerprinting of RNase T1-resistant oligonucleotides, RNA-cDNA hybridization and in vitro translation. A28S RNA species, of 5700 nucleotides, was identified as MC29- or MH2-specific. MC29 RNA shared 4 out of about 17 and MH2 RNA at least 1 out of 16 T1-oligonucleotides with several other avain tumor virus RNAs. In addition MC29 and MH2 RNAs shared 2 oligonucleotides which were not found in any other viral RNA tested. 60% of each 28S RNA could be hybridized by DNA complementary to other avian tumor virus RNAs (group-specific) but 40% could only be hybridized by homologous cDNA (specific). Src gene-related sequences of Rous sarcoma virus were not found in MC29 or MH2 RNA. The specific and group-specific sequences of MC29, defined in terms of their T1-oligonucleotides, were located on a map of all T1-oligonucleotides of viral RNA. Specific sequences mapped between 0,4 and 0,7 map units from the 3'poly(A) end and group-specific sequences mapped between 0 and 0,4 and 0,7 and 1 map units. The MC29-specific RNA segment was represented by 6 oligonucleotides, two of which were those shared only by MC29 and MH2 RNAs. In vitro translation of MC29 RNA generated a major 120 000 dalton protein and minor 56 000 and 37 000 dalton proteins. The 120 000 dalton protein shared sequences with the proteins of the avian tumor viral gag gene, which maps at the 5' end of independently replicating viruses. Since a gag gene-related oligonucleotide was also found near the 5' end of MC29 RNA, we propose that the 120 000 MC29 protein was translated from the 5' 60% of MC29 RNA. It would then include sequences of the defective gag gene as well as MC29-specific sequences. Since both MC29 and MH2 lack the src (sarcoma) gene of Rous sarcoma virusk it is concluded that they contain a distinct class of transforming (onc) genes. We propose that the specific sequences of MC29 and MH2 represent all, or part of, their onc genes because the onc genes of MC29 and MH2 are specific and represent the only known genetic function of these viruses. If this proposal is correct, the onc genes of MC29 and MH2 would be related, because the specific RNA sequence of MC29 shares 2 of 6 oligonucleotides with MH2. It would also follow that the 120 000 dalton MC29 protein is a probable onc gene product, because it is translated from MC29-specific (and group-specific) sequences and because both MC29- and MH2-transformed cells contain specific 120 000 and 100 000 dalton proteins, respectively.

The in vitro of Rous sarcoma virus RNA and function of the viral protein during the viral replication

The gag gene and pol gene of the Rous sarcoma virus are translated in vitro from the 35S viral RNA. The env gene cannot be translated in vitro from the 35S RNA. For the in vitro translation of the src gene. 3' end fragments of the viral RNA are used. The gag protein p15 has a proteolytic activity and specifically processes its own protein precursor pr76. The gag protein p19 suppresses the in vitro translation of the pol gene.

Regulation of mouse mammary tumor virus gene expression by glucocorticoid hormones

Several laboratories have documented that glucocorticoid hormones markedly stimulate the expression of mouse mammary tumor virus genes in a variety of mouse mammary tumor cells and in infected heterologous cells. The effect of the hormone appears to be a rapid and specific augmentation of the synthesis of viral RNA, mediated by interaction with glucocorticoid receptor proteins. The availability of virus-specific reagents and recent developments in the molecular biology of RNA tumor viruses now permit a highly refined analysis of hormonal regulation in this experimental system.

Specific RNA sequences and gene products of MC29 avian acute leukemia virus

The 28S RNA of the defective avian acute leukemia virus MC29 contains two sets of sequences: 60% are hybridized by DNA complementary to other avian tumor virus RNAs (group-specific cDNA) and 40% are hybridized only by MC29-specific cDNA. Specific and group-specific sequences of viral RNA, defined in terms of their large RNase T(1)-resistant oligonucleotides, were located on a map of all large T(1) oligonucleotides of viral RNA. Oligonucleotides representing MC29-specific sequences of viral RNA mapped between 0.4 and 0.7 unit from the 3'-poly(A) end. Oligonucleotides of group-specific sequences mapped between 0 and 0.4 and between 0.7 and 1 map unit. Cell-free translation of viral RNA yielded three proteins with approximate molecular weights of 120,000, 56,000, and 37,000, termed P120(mc), P56(mc), and P37(mc). P120(mc) contained both MC29-specific peptides and serological determinants and peptides of the conserved, internal group-specific antigens of avian tumor viruses. P120(mc) is translated only from full-length 28S RNA. Furthermore, MC29 RNA contains sequences related to the group-specific antigen gene (gag), near the 5' end, which are followed by MC29-specific sequences. We conclude that this protein is translated from the 5' 60% of the RNA, and that it includes a segment translated from the specific sequences. It is suggested that the transforming (onc) gene of MC29 may consists of the specific and some group-specific RNA sequences and that P120(mc), which is also found in transformed cells, may be the onc gene product.

Purification of virus-specific RNA from chicken cells infected with avian sarcoma virus: identification of genome-length and subgenome-leghth viral RNAs

Avian sarcoma virus (ASV)-specific RNA was purified from ASV-infected cells by using hybridization techniques which employ polydeoxycytidylic acid-elongated DNA complementary to ASV RNA as well as chromatography on polyinosinic acid-Sephadex columns. The purity and nucleotide sequence composition of purified, virus-specific RNA were established by rehybridization experiments and analysis of labeled RNase T1-resistant oligonucleotides by two-dimensional polyacrylamide gel electrophoresis. Polyadenylic acid-containing RNA purified from ASV-infected cells contained approximately 1 to 4% virus-specific RNA, compared with 0.06 to 0.15% observed in uninfected cells. Sucrose gradient analysis of virus-specific RNA isolated from ASV-infected cells revealed two major classes of polyadenylated viral RNA with sedimentation values of 36S and 26-28S. Cells infected with transformation-defective ASV (virus containing a deletion of the sarcoma gene) contained 34S and 20-22S viral RNA species. Double-label experiments employing infected cells labeled initially for 48 h with [3H]uridine and then for either 30, 60, or 240 min with [32P]phosphate showed that the intracellular accumulation of genome-length RNA (36S) was significantly faster than that of the 26-28S viral RNA species.

Proteins of Rous-associated virus 61, an avian retrovirus: common precursor for glycoproteins gp85 and gp35 and use of pactamycin to map translational order of proteins in the gag, pol, and env genes

Cells infected by Rous-associated virus 61 (RAV-61) contained a precursor-like protein, pr90, that was specifically precipitated by antiserum directed against envelope glycoproteins, gp85 and gp35. Tryptic peptide mapping showed that pr90 contained tryptic sequences of both gp85 and gp35. Pactamycin mapping experiments indicated that the two glycoproteins are translated from the env-mRNA in the order (5') gp85--gp35. The pactamycin mapping experiments also indicated a translational order of p10--(p27, p12)--p15 for the gag proteins; this agreement with the order previously reported from tryptic mapping studies on precursor pr76 of avian myeloblastosis virus implied that the stoichiometry of the core proteins was unchanged when virions were assembled in the presence of pactamycin. The reverse transcriptase proteins, unlike those of the env and gag genes, fell on the right side of the pactamycin map. This result is in accord with the idea that most, if not all, of the reverse transcriptase protein is translated by read-through of the gag(pol) message rather than by translation of a hypothetical pol-mRNA devoted solely to synthesis of that protein.

Analysis of cytoplasmic RNA and polyribosmomes from feline leukemia virus-infected cells

Cytoplasmic virus-specific RNA and polyribosomes from a chronically infected feline thymus tumor cell line, F-422, were analyzed by using in vitro-synthesized feline leukemia virus (Rickard strain) (R-FeLV) complementary DNA (cDNA) probe. By hybridization kinetics analysis, cytoplasmic, polyribosomat, and nuclear RNAs were found to be 2.1, 2.6, and 0.7% virus specific, respectively. Size classes within subcellular fractions were determined by sucrose gradient centrifugation in the presence of dimethyl sulfoxide followed by hybridization. The cytoplasmic fraction contained a 28S size class, which corresponds to the size of virion subunit RNA, and 36S, 23S, and 15 to 18S RNA species. The virus-specific 36S, 23S, and 15 to 18S species but not the 28S RNA were present in both the total and polyadenylic acid-containing polyribosomal RNA. Anti-FeLV gamma globulin bound to rapidly sedimenting polyribosomes, with the peak binding at 400S. The specificity of the binding for nascent virus-specific protein was determined in control experiments that involved mixing polyribosomes with soluble virion proteins, absorption of specific gamma globulin with soluble virion proteins, and puromycin-induced nascent protein release. The R-FeLV cDNA probe hybridized to RNA in two polyribosomal regions (approximately 400 to 450S and 250S) within the polyribosomal gradients before but not after EDTA treatment. The 400 to 450S polyribosomes contained three major peaks of virus-specific RNA at 36S, 23S, and 15 to 18S, whereas the 250S polyribosomes contained predominantly 36S and 15 to 18S RNA. Further experiments suggest that an approximately 36S minor subunit is present in virion RNA.

Synthesis and glycosylation of polyprotein precursors to the internal core proteins of Friend murine leukemia virus

Synthesis and post-translational processing of murine leukemia virus proteins were analyzed in a murine cell line (Eveline) that produces large amounts of Friend lymphatic leukemia virus. Immunoprecipitation of l-[(35)S]methionine-labeled cell extracts demonstrated that several different virus-specific proteins antigenically related to the virion core (gag) proteins p12 and p30 become radioactive within 1 min of labeling and exhibit labeling kinetics characteristic of primary translation products. The most abundant of these were proteins with molecular weights of 75,000 and 65,000. There were, in addition, two large glycosylated polyproteins with apparent molecular weights of 220,000 and 230,000, which were precipitated by antisera to p30 or p12 but not by antiserum to the major envelope glycoproteins gp69/71. Several lines of evidence, including labeling with d-[(3)H]glucosamine and binding to insolubilized lectins, suggested that the 75,000-dalton internal core polyprotein is slowly processed to form a glycoprotein with an apparent molecular weight of 93,000. On the contrary, the 65,000-dalton protein appeared to be an immediate precursor to the virion core proteins. Its processing can involve intermediates containing p30 and p12 antigens with molecular weights of 50,000 and 40,000; however, the latter did not appear to be obligatory intermediates. The detection of the 40,000-dalton protein suggested that the genes for p30 and p12 are adjacent on the viral genome. These results indicated that there are several pathways of synthesis and post-translational processing of polyprotein precursors to the gag proteins and that several of these polyproteins are glycosylated. A comparison of gag precursor processing in rapidly growing, slowly growing, and stationary cells indicated that different pathways are favored under different conditions of cell growth. Our analysis of envelope glycoprotein synthesis has confirmed the existence of two rapidly labeled 90,000-dalton glycoproteins, which appear to be precursors to the envelope glycoproteins gp69/71.

Translation of 35S and of subgenomic regions of avian sarcoma virus RNA

Rabbit antiserum monospecific for an internal structural protein, p27, of avian sarcoma viruses (ASV) was found to immunoprecipitate polypeptides with molecular weights (Mr) of 180,000 and 76,000 from cell-free reticulocyte lysates programmed by ASV 35S RNA and also from lysates of ASV-infected cells. In addition, the Mr 180,000 protein was also precipitated by antiserum raised against virion DNA polymerase, suggesting that is a product of the two genes nearest the 5' end of virion 35S RNA. We have also investigated the ability of subgenomic portions of virion RNA to program cell-free protein synthesis. A 10-12S poly(A)-containing fragment of RNA from both nondefective and transformation-defective ASV directed the synthesis of a polypeptide of Mr 29,000 immunologically unrelated to the gs antigens; 20-24S poly(A)-containing RNA from nondefective ASV directed the synthesis of a polypeptide of Mr 60,000 not found when a similar RNA preparation from transformation-defective ASV was translated, suggesting that it is the product of the ASV src gene. These results indicate that internal initiation sites for protein synthesis exist on the 35S RNA genome.

Size and genetic content of viral RNAs in avian oncovirus-infected cells

Viral complementary DNA (cDNA) sequences corresponding to the gag, pol, env, src, and c regions of the Rous sarcoma virus genome were selected by hybridizing viral cDNA to RNA from viruses that lack the env or src gene or to polyadenylic acid [poly(A)]-containing RNA fragments of different lengths and isolating either hybridized or unhybridized DNA. The specificities, genetic complexities, and map locations of the selected cDNA's were shown to be in good agreement with the size and map locations of the corresponding viral genes. Analyses of virus-specific RNA, using the specific cDNA's as molecular probes, demonstrated that oncovirus-infected cells contained genome-length (30-40S) RNA plus either one or two species of subgenome-length viral RNA. The size and genetic content of these RNAs varied, depending on the genetic makeup of the infecting virus, but in each case the smaller RNAs contained only sequences located near the 3' end of the viral genome. Three RNA species were detected in Schmidt-Ruppin Rous sarcoma virus-infected cells: 39S (genome-length) RNA; 28S RNA, with an apparent sequence of env-src-c-poly(A); and 21S RNA, with an apparent sequence of src-c-poly(A). Cells infected with the Bryan high-titer strain of Rous sarcoma virus, which lacks the env gene, contained genome-length (35S) RNA and 21S src-specific RNA, but not the 28S RNA species. Leukosis virus-infected cells contained two detectable RNA species: 35S (genome-length) RNA and 21S RNA, with apparent sequence env-c-poly(A). Since gag and pol sequences were detected only in genome-length RNAs, it seems likely that the full-length transcripts function as mRNA for these two genes. The 28S and 21S RNAs could be the active messengers for the env and src genes. Analyses of sequence homologies among nucleic acids of different avian oncoviruses demonstrated substantial similarities within most of the genetic regions of these viruses. However, the "common" region of Rous-associated virus-0, an endogenous virus, was found to differ significantly from that of the other viruses tested.

Frog oocytes synthesize and completely process the precursor polypeptide to virion structural proteins after microinjection of avian myeloblastosis virus RNA

After microinjection of Xenopus laevis oocytes with RNA from avian myeloblastosis virus, viral structural proteins p27, p19, p15, and p12 are formed by a sequence of posttranslational cleavages of a high-molecular-weight precursor polypeptide. The 60-70S RNA aggregate or its 30-40S RNA subunits obtained by heat or formamide treatment possess the same ability to serve as template in X. laevis oocytes. The processing pattern of virus-specific precursor polypeptides is the same in X. laevis oocytes as in chick embryo fibroblasts infected with avian myeloblastosis virus, but the processing takes place at a much slower rate.

In vitro translation yields a possible Rous sarcoma virus src gene product

In vitro translation of Rous sarcoma virus (RSV) virion RNA in the messenger-dependent reticulocyte lysate system yielded polypeptides that were not synthesized by translation of RNA from a transformation-defective deletion mutant of RSV. These RSV-specific products migrated on sodium dodecyl sulfate/polyacrylamide gels as two doublets of approximately 25,000 and 17,000 daltons. Synthesis of these proteins was not sensitive to inhibition by m7GTP; however, synthesis of the 76,000-dalton precursor of the internal structural proteins was sensitive to inhibition by m7GTP. Tryptic peptide maps showed the 25,000- and 17,000-dalton proteins to be related to one another but to be distinct from the 76,000-dalton protein. The 25,000-dalton protein was translated only from a polyadenylylated RNA of approximately 2500 nucleotides, whereas the 76,000-dalton protein was translated from 38S RNA, corresponding to the entire viral genome. A 180,000-dalton protein was also synthesized from 38S RSV virion RNA. From the absence of the 25,000- and 17,000-dalton proteins in the translation products of transformation-defective RSV RNA and the size of their RNA templates, we conclude that these proteins may be derived from coding sequences within the RSV src gene.

Cell-free synthesis of two proteins unique to RNA of transforming virions of Rous sarcoma virus

We have utilized a reticulocyte lysate system to translate the 35S RNA of Rous sarcoma virus. Autoradiograms of the protein products separated on sodium dodecyl sulfate/polyacrylamide gels reveal a heterogeneous mixture of proteins of sizes ranging from 13,000 to 180,000 daltons. In comparing the translational products from 35S RNA of Prague B Rous sarcoma virus with those formed from the RNA of a transformation-defective deletion mutant derived from Prague B, we have found that two proteins, 25,000 and 18,000 daltons, are missing from the latter. Neither of these proteins is immunoprecipitated by monospecific antisera against the structural proteins of avian RNA tumor viruses. The combined atomic mass of 43,000 daltons corresponds to the amount of genetic coding capacity (40,000-50,000 daltons in terms of protein products) deleted from the RNA of the transformation-defective viruses. We propose that these proteins are coded for by the putative oncogene (onc) or sarc (src) gene and that one or both of them may be responsible for the oncogenic transformation caused by these viruses in infected cells.

Identification of Rauscher murine leukemia virus-specific mRNAs for the synthesis of gag- and env-gene products

Polyadenylylated mRNA isolated from cells infected with Rauscher murine leukemia virus was fractionated by centrifugation in in a denaturing sucrose gradient into different sizes. Each RNA fraction was injected into oocytes of Xenopus laevis and the virus-specific products were analyzed by immunoprecipitation with polyvalent and monospecific antisera against polypeptides of Rauscher murine leukemia virus, and then by gel electrophoresis and scintillation autoradiography. It was shown that a 35S mRNA species directs the synthesis of a precursor of the internal or group-specific antigens of the virion (the gag-gene products). A 22S mRNA species directs the synthesis of two viral envelope polypeptides and their precursor polypeptide (env-gene products). The results indicate that the gag- and env-related polypeptides of Rauscher murine leukemia virus are synthesized uncoordinately and provide evidence for open and closed cistrons on the virus-specific mRNAs.

Microinjection analysis of envelope-glycoprotein messenger activities of avian leukosis viral RNAs

Virion RNA from the avian leukosis virus Rous-associated virus 2 (RAV-2) and poly(A)-containing RNAs from RAV-2-infected chick embryo fibroblasts were microinjected into fibroblasts transformed by the Bryan high-titer strain of Rous sarcoma virus (RSV), which is deficient in viral envelope glycoprotein. Production of infectious RSV following these injections depended upon the viral envelope-messenger activity of the injected RNA. This system constituted a sensitive and rigorous assay system for viral envelope-messenger RNA. It was found that 21S mRNA from RAV-2-infected cells expressed the highest activity, while 35S mRNA expressed comparatively little. In addition, RAV-2-virion RNA expressed little messenger activity. The rate of formation of infectious RSV following 21S mRNA injections reached a peak near 9 hr, which was followed by a rapid decline. Evidence has been obtained that a small fraction of both 35S virion RNA and 35S mRNA from virus-infected cells was encapsulated into virus particles following their injection into virus-producing cells.

Nucleotide sequence at the 5' terminus of the avian sarcoma virus genome

Transcription of DNA from the RNA genome of avian sarcoma virus by RNA-directed DNA polymerase in vitro initiates on a primer (tRNATrp) located near the 5'-terminus of the viral genome. One of the major products of transcription is a single-stranded DNA chain complementary to a sequence of 101 nucleotides immediately distal to the site of initiation of DNA synthesis. We have determined the complete nucleotide sequence of this transcribed chain for the Prague strain of avian sarcoma virus, a partial sequence of the transcribed chain for the Bratislava 77 strain of avian sarcoma virus, and the sequence of a DNA transcript that is shorter than the transcribed single-stranded chain. Our data define the location of tRNATrp on the genome of avian sarcoma virus and provide the sequence of 119 nucleotides at the 5'-terminus of the genome. Portions of this sequence may be involved in the binding of RNA-directed DNA polymerase, the initiation of translation from viral messenger RNA, the extension of RNA-directed DNA synthesis from the 5'- to the 3'-terminus of viral RNA, and the integration of viral DNA into the host genome.

Analysis of intracellular feline leukemia virus proteins II. Generation of feline leukemia virus structural proteins from precursor polypeptides

The synthesis and processing of feline leukemia virus (FeLV) polypeptides were studied in a chronically infected feline thymus tumor cell line, F-422, which produces the Rickard strain of FeLV. Immune precipitation with antiserum to FeLV p30 and subsequent sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) were used to isolate intracellular FeLV p30 and possible precursor polypeptides. SDS-PAGE of immune precipitates from cells pulse-labeled for 2.5 min with [35S]methionin revealed the presence of a 60,000-dalton precursor polypeptide (Pp60) as well as a 30,000-dalton polypeptide. When cells were grown in the presence of the proline analogue L-azetidine-2-carboxylic acid, a 70,000-dalton precursor polypeptide (Pp70) was found in addition to Pp60 after a 2.5-min pulse. The cleavage of Pp60 could be partially inhibited by the general protease inhibitor phenyl methyl sulfonyl fluoride (PMSF). This partial inhibition was found to occur only if PMSF was present during pulse-labeling. Intracellular Pp70 and Pp60 and FeLV virion p70, p30, p15, p11, and p10 were subjected to tryptic peptide analysis. The results of this tryptic peptide analysis demonstrated that intracellular Pp70 and virion p70 were identical and that both contained the tryptic peptides of FeLV p30, p15, p11, and p10. Pp60 contained the tryptic peptides of FeLV P30, P15, and P10, but lacked the tryptic peptides of P11. The results of pactamycin gene ordering experiments indicated that the small structural proteins of FeLV are ordered p11-p15-p10-p30. The data indicate that the small structural proteins of FeLV are synthesized as part of a 70,000-dalton precursor. A cleavage scheme for the generation of FeLV p70, p30, p15, p11, and p10 from precursor polypeptides is proposed.

Rous sarcoma virus genome is terminally redundant: the 5' sequence

When Rous sarcoma virus RNA is transcribed into DNA by the reverse transcriptase, a tRNA primer is elongated into DNA. The primer is near the 5' end of the virus genome; the first major DNA made is a "run-off" product extending 101 bases from the primer to the 5' end of the template. We have studied this DNA molecule to determine the sequence of the first 101 bases at the 5' end of the Rous sarcoma virus genome (Prague strain, subgroup C). Twenty-one bases at the extreme 5' end are also at the 3' end of the virus genome (see D. E. Schwartz, P. C. Zamecnik, and H. L. Weith, this issue, pp. 994-998), and thus this virus is terminally redundant. The existence of this sequence repetition immediately suggests mechanisms by which the growing DNA copy can jump from the 5' end to a 3' end of the template and become circular. The sequence also displays a possible ribosome binding site and enough secondary structure to permit a possible 5'-5' linkage of viral RNA molecules.

Cleavage of Rous sarcoma viral polypeptide precursor into internal structural proteins in vitro involves viral protein p15

The polypeptide precursor pr76 to the internal viral group specific (gs) antigen proteins of Rous sarcoma virus, synthesized in a cell-free system of ascites cells, has been processed in vitro into the viral proteins by purified viral protein p15 as well as by disrupted Rous sarcoma virus. Disrupted Rauscher murine leukemia virus does not stimulate the cleavage process in vitro. Autocatalytic cleavage of the polypeptide precursor pr76 or Rous sarcoma virus, which contains the peptide sequence of p15, is not observed.