Conditional lethal mutants of adenovirus 2-simian virus 40 hybrids. I. Host range mutants of Ad2+ND1

Design of new genome- and gene-sourced primers and identification of QTL for seed oil content in a specially high-oil Brassica napus cultivar

Rapeseed (Brassica napus L.) is one of most important oilseed crops in the world. There are now various rapeseed cultivars in nature that differ in their seed oil content because they vary in oil-content alleles and there are high-oil alleles among the high-oil rapeseed cultivars. For these experiments, we generated doubled haploid (DH) lines derived from the cross between the specially high-oil cultivar zy036 whose seed oil content is approximately 50% and the specially low-oil cultivar 51070 whose seed oil content is approximately 36%. First, to address the deficiency in polymorphic markers, we designed 5944 pairs of newly developed genome-sourced primers and 443 pairs of newly developed primers related to oil-content genes to complement the 2244 pairs of publicly available primers. Second, we constructed a new DH genetic linkage map using 527 molecular markers, consisting of 181 publicly available markers, 298 newly developed genome-sourced markers and 48 newly developed markers related to oil-content genes. The map contained 19 linkage groups, covering a total length of 2,265.54 cM with an average distance between markers of 4.30 cM. Third, we identified quantitative trait loci (QTL) for seed oil content using field data collected at three sites over 3 years, and found a total of 12 QTL. Of the 12 QTL associated with seed oil content identified, 9 were high-oil QTL which derived from the specially high-oil cultivar zy036. Two high-oil QTL on chromosomes A2 and C9 co-localized in two out of three trials. By QTL mapping for seed oil content, we found four candidate genes for seed oil content related to four gene markers: GSNP39, GSSR161, GIFLP106 and GIFLP046. This information will be useful for cloning functional genes correlated with seed oil content in the future.

Differential ability of two simian virus 40 strains to induce malignancies in weanling hamsters

Different strains of simian virus 40 (SV40) exist and are associated with some human malignancies, but it is not known if SV40 strains differ in biological potential in vivo. In two long-term experiments, Syrian golden hamsters 21 days of age were inoculated by the intraperitoneal route with two different strains of SV40 (10(7) plaque-forming units/animal) and were followed for 8 or 12 months. In vivo responses to strain VA45-54, isolated originally from monkey kidney cells, and to strain SVCPC, recovered from human cancers, were compared. Control animals of the same age were inoculated intraperitoneally with cell culture media. Malignancies developed only in animals infected with SV40 and not in controls. The rate of tumor development was more frequent among animals infected with strain SVCPC than with VA45-54, both in experiments held for 8 months (11/22, 50% vs. 4/20, 20%) and for 12 months (7/15, 47% vs. 3/13, 23%). Histologically, the tumors resembled mesotheliomas, osteosarcoma, and poorly differentiated sarcomas. Metastases to lung and lymph nodes occurred with both viral strains. T-antigen expression was detected in most tumor cells by immunohistochemistry. Anti-T-antigen antibodies were produced by almost all tumor-bearing animals and by about two-thirds of those that did not develop tumors after virus inoculation. SV40 viral neutralizing antibodies were detected in all tumor-bearing animals and in 92% and 38% of those inoculated with SVCPC and VA45-54, respectively, that failed to develop tumors. Antibody titers were usually higher in animals with tumors than in those without. Control animals did not develop viral antibodies. Infectious virus was recovered from 2 of 15 tumors tested. This study showed that there are biological differences between these two SV40 strains that influence the outcome of infections in normal hosts, including the development of malignancies and neutralizing antibody, and proved the principle that SV40 strains from different clades can vary in biological properties in vivo.

Emergent human pathogen simian virus 40 and its role in cancer

The polyomavirus simian virus 40 (SV40) is a known oncogenic DNA virus which induces primary brain and bone cancers, malignant mesothelioma, and lymphomas in laboratory animals. Persuasive evidence now indicates that SV40 is causing infections in humans today and represents an emerging pathogen. A meta-analysis of molecular, pathological, and clinical data from 1,793 cancer patients indicates that there is a significant excess risk of SV40 associated with human primary brain cancers, primary bone cancers, malignant mesothelioma, and non-Hodgkin's lymphoma. Experimental data strongly suggest that SV40 may be functionally important in the development of some of those human malignancies. Therefore, the major types of tumors induced by SV40 in laboratory animals are the same as those human malignancies found to contain SV40 markers. The Institute of Medicine recently concluded that "the biological evidence is of moderate strength that SV40 exposure could lead to cancer in humans under natural conditions." This review analyzes the accumulating data that indicate that SV40 is a pathogen which has a possible etiologic role in human malignancies. Future research directions are considered.

Simian virus 40 large T antigen host range domain functions in virion assembly

The simian virus 40 (SV40) T antigen host range mutants dl1066 and dl1140 display a postreplicative block to plaque formation which suggests a novel role for T antigen late in the viral life cycle. The host range mutants dl1066 and dl1140 are able to grow in and plaque on BSC but not on CV1 monkey kidney cells, a normally permissive host. Previous work showed that in CV1 cells infected with dl1066 and dl1140, levels of viral DNA replication and of late capsid protein accumulation were only slightly reduced and the failure to accumulate agnoprotein was not likely to be the major factor responsible for the mutants' growth defect. Here we show that the host range mutants are defective in the assembly of viral particles. SV40 assembly proceeds as the progressive conversion of 75S viral chromatin complexes to 200S-240S assembled virions. When virus-infected cell extracts are separated on 5 to 40% sucrose gradients, wild-type extracts show the greatest accumulation of viral late protein in the 200S-240S fractions corresponding to the assembled virus peak and lesser amounts in the 75S-150S fractions corresponding to immature assembly intermediates. The host range mutants dl1066 and dl1140 grown in nonpermissive CV1 cells, however, failed to assemble any appreciable amounts of mature 200S-240S virions and accumulate 75S intermediates, whereas in permissive BSC cells, levels of assembly were more slightly reduced than those of the wild type. Analysis of the protein composition of gradient fractions suggests that SV40 assembly proceeds by a mechanism similar to that proposed for polyomavirus and suggests that the host range blockage may result from a failure of such mutants to add VP1 to 75S assembly intermediates.

Association of p53 binding and immortalization of primary C57BL/6 mouse embryo fibroblasts by using simian virus 40 T-antigen mutants bearing internal overlapping deletion mutations

To more precisely map the immortalization and p53 binding domains of T antigen, a large series of overlapping deletion mutations were created between codons 251 to 651 by utilizing a combination of Bal 31 deletion and oligonucleotide-directed mutagenesis. Immortalization assay results indicated that amino acids (aa) 252 to 350, 400, and 451 to 532 could be removed without seriously compromising immortalization, although the appearance of immortal colonies was delayed in some cases. Western immunoblotting experiments indicated that the p53 binding capacities of T antigen produced by mutants missing aa 252 to 300, 301 to 350, 400, or 451 to 532 were only slightly reduced relative to that of wild-type T antigen. Within the limits of this deletion analysis, the immortalization and p53 binding domains appear to be colinear and, in fact, may represent two aspects of the same domain. This deletion analysis eliminates the entire zinc finger domain (aa 302 to 320), a small portion of the leucine-rich region (aa 345 to 350), and a large portion of the ATP binding domain (aa 451 to 528) as participants in p53 binding or in the immortalization process. The results also show that removal of T antigen amino acids within the region 451 to 532 appears to alter the capacity of newly synthesized but not older T antigen and p53 molecules to form complexes.

Increased permissivity of monkey cells to human adenovirus multiplication is affected by culturing conditions and correlates with both synthesis of virion fiber protein and altered splicing of its mRNA

Human adenoviruses (Ad2) grow poorly in CV-1 (monkey) cells, resulting in an abortive infection. During abortive infections synthesis of the fiber protein is approximately 100-fold depressed compared to its synthesis in CV-1 cells productively infected with a host range mutant of adenovirus (Ad2hr400), while the corresponding mRNA is reduced only 10-fold. We found that passage of CV-1 cells under modified culture conditions resulted in loss of restrictiveness for Ad2 growth. As cells became more permissive, fiber polypeptide synthesis was enhanced although fiber mRNA levels did not necessarily increase. Analysis of the 5' ends of fiber message isolated from cells in various stages of permissivity showed a direct correlation between efficient synthesis of the fiber protein and an altered splicing pattern of the fiber message.

Comparison of human and monkey cells for the ability to attenuate transcripts that begin at the adenovirus major late promoter

Late transcription from the adenovirus major late promoter can terminate prematurely at a site 182 to 188 nucleotides downstream. Experiments have been designed, with run-on transcription in nuclei in vitro or riboprobe protection of RNA obtained both in vivo and in vitro, that demonstrate that the ratio of attenuator RNA to readthrough RNA is greater in monkey cells (CV-1) than in human cells (HeLa). This may explain, in part, why the human adenoviruses replicate more poorly in CV-1 cells than in HeLa cells. A mutant adenovirus that replicates better than wild-type virus in monkey cells produces less of the attenuator RNA than wild-type adenovirus does in monkey cells. Monkey cell extracts have been shown to contain a factor that, when added to human cell extracts transcribing adenovirus DNA in vitro, increases the production of attenuator RNA in these reactions. These observations help to explain a portion of the block to the production of infectious adenoviruses in monkey cells.

The adenovirus type 2 DNA-binding protein interacts with the major late promoter attenuated RNA

The adenovirus 72-kilodalton DNA-binding protein (DBP) binds to the attenuated RNA derived from the viral major late promoter. Protection from T1 RNase digestion can be observed when DBP is incubated with attenuated RNA. By using attenuated RNA labeled at one end, the T1 RNase digestion pattern can be mapped to residues located at specific sites in this RNA. Heterologous competitor RNAs do not alter the pattern of DBP protection of a labeled attenuated RNA, as does the identical attenuated RNA. These data indicate some specificity of the interaction between DBP and attenuated RNA. Adenovirus infection of monkey cells results in a more efficient attenuation of RNA initiated at the major late promoter and a reduced level of infectious virus. Adenovirus mutations in DBP relieve this restriction. These DBP mutant proteins do not change their binding properties to the attenuated RNA but suggest a mechanism by which DBP plays a role in the adenovirus host range restriction in monkey cells.

Chinese hamster ovary cells replicate adenovirus deoxyribonucleic acid

Chinese hamster ovary (CHO) cells infected with adenovirus type 2 (Ad2) produced amounts of viral deoxyribonucleic acid (DNA) equal to that synthesized in permissively infected HeLa cells. However, there was 6,000-fold less virion produced in CHO cells. Since the structural viral polypeptides were not detected by pulse-labeling CHO cells at various times postinfection, the block in virion formation is located between the synthesis of viral DNA and late proteins. Extracts of CHO cells could also function in a recently reported in vitro Ad2 DNA synthesis system which is dependent upon the addition of exogenous Ad2 DNA covalently linked to a 5'-terminal protein (Ikeda et al., Proc. Natl. Acad. Sci. U.S.A. 77:5827-5831, 1980). Extracts of infected CHO cytoplasm were able to complement uninfected CHO nuclear extracts to synthesize viral DNA on Ad2 templates. This in vitro replication system has the potential to probe host DNA synthesis requirements as well as viral factors.

Suppression of the translation defect phenotype specific for a virus-associated RNA-deficient adenovirus mutant in monkey cells by simian virus 40

Human cells infected with adenovirus type 2 (Ad2) or Ad5 require VAI RNA for efficient translation of viral mRNAs at late times after infection. The Ad5 mutant dl-sub720 synthesized neither virus-associated I (VAI) nor VAII RNAs, and infection of human cells with this mutant resulted in reduced virion polypeptide synthesis. Infection of monkey cells with this mutant also resulted in drastic reduction of polypeptide synthesis compared with wild-type (WT) adenovirus infections. Steady-state levels of hexon-specific mRNA were found to be comparable in WT- and mutant-infected monkey cells. The in vitro translation experiments showed that double-mutant- and WT-infected cells contained comparable levels of translatable hexon mRNA (and other adenovirus late mRNAs), suggesting that the severe inhibition of hexon protein synthesis in the VA mutant involves a translation block. Preinfection of monkey cells with simian virus 40 fully restored the efficient translation of this mRNA in the VA mutant infections to the level observed in WT-infected cultures. These results raise the possibility that simian virus 40 may encode or induce factors that suppress the translation block that occurs during adenovirus infections in the absence of the VA RNAs.

Synthesis of the Ad2+ND5-specified 42K protein is regulated posttranscriptionally in abortively infected monkey cells

In abortive infections of monkey cells by Ad2+ND5, the synthesis of the simian virus 40-specific 42,000-molecular-weight (42K) protein was reduced approximately 10-fold compared with a productive coinfection by Ad2+ND5 plus Ad2hr400 and about 20-fold compared with productive infections by Ad2+ND5 plus simian virus 40 or by Ad2+ND2 alone. However, the level of Ad2+ND5-specific mRNA was depressed twofold or less in abortive infections compared with productive infections. Moreover, the 42K mRNA isolated from abortive Ad2+ND5 infections translated in vitro with the same efficiency as the mRNA isolated from productive coinfections. This is analogous to the block to synthesis of the adenovirus fiber polypeptide in monkey cells (Anderson and Klessig, J. Mol. Appl. Genet. 2:31-43, 1983). Also like fiber protein, the increased level of the 42K protein found in productive infections was due to enhanced synthesis, not increased stability of the protein. Our results suggest that the synthesis of the Ad2+ND5-specified 42K protein and the adenovirus fiber protein are regulated in similar posttranscriptional manners.

Similar regulation of the synthesis of adenovirus fiber and of simian virus 40-specific proteins encoded by the helper-defective Ad2+SV40 hybrid viruses Ad2+ND5 and Ad2+ND4del

Human adenoviruses fail to multiply effectively in monkey cells. The block to the replication of these viruses can be overcome by coinfection with simian virus 40 (SV40) or when part of the SV40 genome is integrated into and expressed as part of the adenovirus type 2 (Ad2) genome, as occurs in several Ad2+SV40 hybrid viruses, such as Ad2+ND1, Ad2+ND2, and Ad2+ND4. The SV40 helper-defective Ad2+SV40 hybrid viruses Ad2+ND5 and Ad2+ND4del were analyzed to determine why they are unable to grow efficiently in monkey cells even though they contain the appropriate SV40 genetic information. Characterization of the Ad2+ND5-SV40-specific 42,000-molecular-weight (42K) protein revealed that this protein is closely related, but not identical, to the SV40-specific 42K protein of the SV40 helper-competent Ad2+ND2 hybrid virus. Although the minor differences between these proteins may be sufficient to account for the poor growth of Ad2+ND5 in monkey cells, the most striking difference between helper-competent Ad2+ND2 and helper-defective Ad2+ND5 is in the production of the SV40-specific protein after infection of monkey cells. Whereas synthesis of the SV40-specific proteins of Ad2+ND2 is very similar in human and in monkey cells, production of the 42K protein of Ad2+ND5 is dramatically reduced in monkey cells compared with human cells. Similarly, the synthesis of the SV40-specific proteins of Ad2+ND4del is markedly reduced in monkey cells. Thus, it is likely that both Ad2+ND5 and Ad2+ND4del are helper defective because of a block in the production of their SV40-specific proteins rather than because their SV40-specific proteins are nonfunctional. This block, like the block to adenovirus fiber synthesis, is overcome by coinfection with SV40, with helper-competent hybrid viruses, or with host range mutants of adenoviruses. This suggests that the synthesis of fiber and the synthesis of SV40-specific proteins are similarly regulated in Ad2+SV40 hybrid viruses.

Restricted changes in the adenovirus DNA-binding protein that lead to extended host range or temperature-sensitive phenotypes

Human adenovirus fails to multiply efficiently in monkey cells owing to a block to late viral gene expression. Ad2hr400 through Ad2hr403 are a set of host range (hr) mutants which were selected for their ability to readily grow in these cells at 37 degrees C. The mutations responsible for this extended host range have previously been mapped to the 5' portion of the gene encoding the 72-kilodalton DNA-binding protein (DBP). DNA sequence analyses indicate that all four hr mutants contain the same alteration at coding triplet 130, which changes a histidine codon to a tyrosine codon. These results extend those of Anderson et al. (J. Virol. 48:31-39, 1983), which suggested that only this change in the DBP amino acid sequence can expand adenovirus host range to monkey cells. The hr phenotype does not appear to require phosphorylation of this tyrosine residue, since no phosphotyrosine was detected in DBP isolated from Ad2hr400-infected monkey cells. The hr mutants Ad2hr400 through Ad2hr403, however, are cold sensitive for growth in monkey cells. The mutant Ad2ts400, which was derived from Ad2hr400, represents a second class of hr mutants which can grow efficiently in monkey cells at 32.5 degrees C. The cold-resistant hr mutation of Ad2ts400 has previously been mapped to the 5' region of the DBP gene (map units 63.6 through 66). DNA sequence analysis of this region shows that this mutant contains the original hr alteration at coding triplet 130 as well as a second alteration at coding triplet 148, which changes an alanine codon to a valine codon. We suspect that the alterations at amino acids 130 and 148 change the structure of the amino-terminal domain of the DBP, allowing it to better interact with monkey cell components required for late viral gene expression. Ad2ts400 also contains a temperature-sensitive mutation which has previously been mapped to the 3' portion of the DBP gene (map units 61.3 through 63.6). Sequence analysis of this region indicates that the DBP coding triplet 413 has been altered. This change from a serine codon to a proline codon is the same alteration reported in the previously sequenced DBP mutants Ad5ts125 (W. Kruijer et al., Nucleic Acids Res. 9:4439-4457, 1981) and Ad5ts107 (W. Kruijer et al., Virology 124:425-433, 1983). Thus it appears that only a very limited number of changes in either the 5' or the 3' portion of the DBP gene can give rise to the hr or temperature-sensitive phenotypes, respectively.

Introduction, stable integration, and controlled expression of a chimeric adenovirus gene whose product is toxic to the recipient human cell

The DNA-binding protein (DBP) encoded by human adenoviruses is a multifunctional polypeptide which plays a central role in regulating the expression of the viral genes. To gain a better understanding of the relationships between the various functions provided by DBP, an extensive collection of DBP mutants is essential. To this end we have constructed several permissive human cell lines which contain and express the DBP gene at high levels to allow propagation of otherwise lethal, nonrecoverable mutants of DBP. Because DBP is toxic to human cells, cell lines were constructed by using a vector in which the DBP gene is under the control of the dexamethasone-inducible promoter of the mouse mammary tumor virus. The low basal levels of DBP synthesis in the absence of dexamethasone allows isolation and propagation of these cells. Addition of dexamethasone enhances DBP production 50- to 200-fold, and within 8 h its synthesis from the single integrated copy of the chimeric gene is 5 to 15% of that observed during peak DBP synthesis in infected human cells in which hundreds of copies of the DBP gene serve as templates. At the nonpermissive temperature, adenovirus mutants with ts lesions in the DBP gene replicate their DNAs, express their late genes, and form infectious viral particles in these DBP+ cell lines but not in the parental HeLa cells.

Introduction, stable integration, and controlled expression of a chimeric adenovirus gene whose product is toxic to the recipient human cell

The DNA-binding protein (DBP) encoded by human adenoviruses is a multifunctional polypeptide which plays a central role in regulating the expression of the viral genes. To gain a better understanding of the relationships between the various functions provided by DBP, an extensive collection of DBP mutants is essential. To this end we have constructed several permissive human cell lines which contain and express the DBP gene at high levels to allow propagation of otherwise lethal, nonrecoverable mutants of DBP. Because DBP is toxic to human cells, cell lines were constructed by using a vector in which the DBP gene is under the control of the dexamethasone-inducible promoter of the mouse mammary tumor virus. The low basal levels of DBP synthesis in the absence of dexamethasone allows isolation and propagation of these cells. Addition of dexamethasone enhances DBP production 50- to 200-fold, and within 8 h its synthesis from the single integrated copy of the chimeric gene is 5 to 15% of that observed during peak DBP synthesis in infected human cells in which hundreds of copies of the DBP gene serve as templates. At the nonpermissive temperature, adenovirus mutants with ts lesions in the DBP gene replicate their DNAs, express their late genes, and form infectious viral particles in these DBP+ cell lines but not in the parental HeLa cells.

Translation of adenovirus 2 late mRNAs microinjected into cultured African green monkey kidney cells

Adenovirus 2-infected monkey cells fail to synthesize fiber, a 62,000 Mr virion polypeptide expressed at late times in productively infected cells. Yet these cells contain fiber mRNA that, after isolation, can be translated in vitro. The reason for the failure of monkey cells to translate fiber mRNA has been approached by microinjecting adenovirus mRNA into the cytoplasm of cultured monkey cells. Late adenovirus 2 mRNA, isolated from infected HeLa cells, was efficiently expressed when microinjected into the African green monkey kidney cell line CV-C. Expressed viral proteins identified by immunoprecipitation included the adenovirus fiber polypeptide. This result demonstrates that the monkey cell translational apparatus is capable of recognizing and expressing functional adenovirus fiber mRNA. Microinjection of late virus mRNA into cells previously infected with wild-type adenovirus 2 failed to increase significantly the yield of infectious virus.

The nucleotide sequence at the recombination/integration sites of the hybrid viruses Ad2+ND3 and Ad2+ND5

The nucleotide sequence at the recombination/integration sites of the adenovirus 2-simian virus 40 hybrid viruses, Ad2+ND3 and Ad2+ND5, is reported. These viruses were obtained by passages through human cells and fail to express the SV40-related proteins. The lack of expression of SV40-related proteins has been explained on the basis of the nucleotide sequence at the recombination sites. Ad2+ND3 has the entire reading frame for the SV40 T antigen removed up to the translation termination codon. The recombination event in Ad2+ND5 was found to occur in the leader region 11 nucleotides upstream from the splice junction, thus totally eliminating the naturally occurring splice site, which might have lead to defective processing of the mRNA. Alternatively, because of the large deletion, this virus is incapable of making similar hybrid proteins as in Ad2+ND1, Ad2+ND2, and Ad2+ND4, which share the N-terminal sequence of the 16-kDa glycoprotein of the wild-type virus. Thus, either one or both of these events may explain the lack of synthesis of the SV40 T antigen specific protein. Ad2+ND3 and Ad2+ND5 share the sequences at the right junction which suggests their origin from a common precursor. Also, the recombination was found to result in the disruption of the poly (A) addition signal of the adenovirus 2 early region III transcripts. All of the junction sequences were found to be rich in A:T base pairs.

The function(s) provided by the adenovirus-specified, DNA-binding protein required for viral late gene expression is independent of the role of the protein in viral DNA replication

The adenovirus type 2 (Ad2) host range mutant Ad2hr400 grows efficiently in cultured monkey cells at 37 degrees C, but is cold sensitive for plaque formation and late gene expression at 32.5 degrees C. After nitrous acid mutagenesis of an Ad2hr400 stock, cold-resistant variants were selected in CV1 monkey cells at 32.5 degrees C. One such variant, Ad2ts400, was also temperature sensitive (ts) for growth in both CV1 and HeLa cells. Marker rescue analysis has been used to show that the two phenotypes, cold resistant and temperature sensitive, are due to two independent mutations, each of which resides in a different segment of the gene encoding the 72-kilodalton DNA binding protein (DBP). The cold-resistant mutation (map coordinates 63.6 to 66) is a host range alteration that enhances the ability of the virus to express late genes and grow productively in monkey cells at 32.5 degrees C. The temperature-sensitive mutation is in the same complementation group and maps to the same segment of the DBP gene (map coordinates 61.3 to 63.6) as the well-characterized DBP mutant Ad5ts125. Like Ad5ts125, Ad2ts400 is unable to replicate viral DNA or to properly shut off early mRNA expression at the nonpermissive temperature. Two sets of experiments with Ad2ts400 suggest that DBP contains separate functional domains. First, when CV1 cells are coinfected at the nonpermissive temperature with Ad2 plus Ad2ts400 (Ad2 allows DNA replication and entry into, but not completion of, the late phase of infection), normal late gene expression and productive growth occur. Second, temperature shift experiments show that, although DNA replication is severely restricted at the nonpermissive temperature in ts400-infected monkey cells, late gene expression occurs normally. These results indicate that the DBP activity required for normal late gene expression in monkey cells is functional even when the DBP's DNA replication activity is disrupted.

Construction of human cell lines which contain and express the adenovirus DNA binding protein gene by cotransformation with the HSV-1 tk gene

We have introduced the DNA binding protein (DBP) gene of human adenovirus type 5 (Ad5) into high molecular weight DNA of permissive human cells by cotransformation of tk- cells with the cloned DBP and HSV-1 thymidine kinase genes. 110 tk+ cell lines were isolated after selection in HAT medium. The amount and arrangement of adenovirus sequences in the tk+ cell lines were analyzed by restriction endonuclease digestion and filter hybridization. Twelve of the 110 lines carry at least a segment of the DBP gene while only three of these contain the entire DBP gene at approximately one copy per cell. Cytoplasmic, polyadenylated DBP mRNA is made in all three cell lines though the amount is very low compared to that present in infected HeLa cells. The cell line U13-2 which contains approximately 1/30 the steady-state level of DBP mRNA found in infected HeLa cells produces a few percent of the amount of DBP made during the peak period of DBP synthesis in infected cells. The other two lines contain lower levels of DBP mRNA and do not synthesize detectable levels of the protein. When these DBP-tk+ cell lines are infected with adenovirus mutants containing temperature-sensitive (ts) mutations in the DBP gene, only U13-2 permits some viral DNA replication (and hence late gene expression) at the nonpermissive temperature, indicating that sufficient quantities of DBP from the integrated gene are produced to allow complementation of the ts mutation in this cell line. However, growth of these ts mutants (as measured by virus production) is only partially complemented in U13-2 at the nonpermissive temperature.

Independent, spontaneous mutants of adenovirus type 2-simian virus 40 hybrid Ad2+ND3 that grow efficiently in monkey cells possess indentical mutations in the adenovirus type 2 DNA-binding protein gene

Four independent, spontaneous mutants of the adenovirus type 2-simian virus 40 hybrid Ad2+ND3 that allow efficient growth in monkey cells were isolated previously (C. W. Anderson, Virology 111:263-269, 1981). All four mutations have been mapped within the coding sequence for the adenovirus DNA-binding protein by marker rescue analysis. DNA sequence analysis of a region of ca. 1,000 base pairs shown by marker rescue to contain the host range mutations demonstrated that the host range mutant hr602 differs from its parent, Ad2+ND3, at only a single nucleotide. Mutant hr602 has a thymine in place of a cytosine at the first position of the 130th codon, as measured from the initiation site for the DNA-binding protein. This change results in the replacement of a histidine by a tyrosine in mutant hr602 DNA-binding protein. Each of the other three Ad2+ND3 host range mutants have exactly the same nucleotide alteration as does hr602. This same nucleotide change was recently reported for a similarly derived host range mutant of adenovirus 5.

Normal translation of human adenovirus mRNA in cell-free lysates prepared from abortively as well as productively infected monkey cells

A variety of mRNAs, including adenovirus-specified mRNAs isolated from infected human cells, were translated with similar efficiencies in S10 cell-free lysates prepared from productively and abortively infected monkey cells. These results may suggest that reduced synthesis of the late viral proteins in abortively infected monkey cells is not due to a defect in the protein-synthesizing apparatus of the cell.

Synthesis of human adenovirus early RNA species is similar in productive and abortive infections of monkey and human cells

Northern (RNA) blot analysis has been used to show that synthesis of early mRNA species is similar in monkey cells productively or abortively infected with human adenovirus. mRNA species from all five major early regions (1A, 1B, 2, 3, 4) are identical in size and comparable in abundance whether isolated from monkey cells infected with adenovirus type 2 or with the host range mutant Ad2hr400 or coinfected with adenovirus type 2 plus simian virus 40. The mRNA species isolated from monkey cells are identical in size to those isolated from human cells. Production of virus-associated RNA is also identical in productive and abortive infections of monkey cells. Synthesis of virus-associated RNA is, however, significantly greater in HeLa cells than in CV1 cells at late times after infection regardless of which virus is used in the infection.

Proteins containing only half of the coding information of early region 1b of adenovirus are functional in human cells transformed with the herpes simplex virus type 1 thymidine kinase gene and adenovirus type 2 DNA

We introduced into tk- human 143 cells adenovirus type 2 (Ad2) genes by transformation with a plasmid (p711) containing both Ad2 sequences and the herpes simplex virus type 1 (HSV-1) tk gene. p711 contained approximately the left 8% of the Ad2 genome inserted in the HindIII site of pBR322, whereas the fragment of HSV-1 containing the tk gene was inserted in the BamHI site. Three tk+ cell lines were isolated after selection in HAT medium. The arrangement of viral sequences in the three transformants was analyzed by restriction endonuclease digestion and filter hybridization. All three lines contained a single insertion of Ad2 DNA which was present at approximately one copy per cell. The arrangement of Ad2 sequences in these lines was identical to that found in the linear p711 DNA used in the transformation. S1 analysis of the Ad2-specified RNA from two of these lines indicated that the early region 1a mRNA's were synthesized, though in lower amounts than found in lytic infections. These cell lines contained only the left half of early region 1b (4.6 to 11.2), which encoded the 5' portion of the 1b mRNA's. A complex pattern of 1b RNAs was made in these cell lines. Transcription of most of these RNAs began at or near the 1b promoter and proceeded through the 1b sequences into the flanking pBR322, HSV-1, or host sequences. Since many of the RNAs were terminated or spliced in the HSV-1 (anti-sense strand) or pBR322 sequences, new RNA processing sites must be used in the formation of these mRNA's. All three lines fully complemented the 1a deletion mutant Ad5 dl312. Surprisingly, these lines also permitted the growth of 1b deletion mutants (Ad5 dl313 and Ad5 dl434), although the complementation was not always complete. Presumably the new gene product(s) which contained only part of the 1b gene provided most of the essential function(s) required for viral multiplication. Alternatively, the 1b 19-kilodalton protein which was entirely encoded by the adenovirus sequences present in these cell lines was sufficient for viral growth even in the absence of the 1b 55-kilodalton protein.

Virus-associated RNAs of naturally occurring strains and variants of group C adenoviruses

We compared the sequences of the virus-associated (VA) RNAs of group C adenoviruses, serotypes 1, 2, 5, and 6, and of three variants of adenovirus type 2 (Ad2) selected for loss of the BamHI restriction site in the VA RNAI gene. In the naturally occurring strains. VA RNAI exists in two forms which differ by two nucleotides: one form is found in Ad2 and Ad6, and the other is found in Ad1 and Ad5. There are three sites of variation in Va RNAII, the Ad1, Ad2, and Ad5 forms each differing from Ad6 VA RNAII at one of the positions. One of the selected variants has a four-base duplication within the BamHI cleavage site, whereas the two others have acquired a VA RNAI sequence indistinguishable from that of Ad5. The findings are interpreted in terms of the secondary structures of the VA RNAs and the interrelationships among the viruses.

Chinese hamster ovary cells replicate adenovirus deoxyribonucleic acid

Chinese hamster ovary (CHO) cells infected with adenovirus type 2 (Ad2) produced amounts of viral deoxyribonucleic acid (DNA) equal to that synthesized in permissively infected HeLa cells. However, there was 6,000-fold less virion produced in CHO cells. Since the structural viral polypeptides were not detected by pulse-labeling CHO cells at various times postinfection, the block in virion formation is located between the synthesis of viral DNA and late proteins. Extracts of CHO cells could also function in a recently reported in vitro Ad2 DNA synthesis system which is dependent upon the addition of exogenous Ad2 DNA covalently linked to a 5'-terminal protein (Ikeda et al., Proc. Natl. Acad. Sci. U.S.A. 77:5827-5831, 1980). Extracts of infected CHO cytoplasm were able to complement uninfected CHO nuclear extracts to synthesize viral DNA on Ad2 templates. This in vitro replication system has the potential to probe host DNA synthesis requirements as well as viral factors.

Adenovirus type 2 expresses fiber in monkey-human hybrids and reconstructed cells

Adenovirus type 2 protein expression was measured by indirect immunofluorescence in monkey-human hybrids and in cells reconstructed from monkey and human cell karyoplasts and cytoplasts. Monkey-human hybrid clones infected with adenovirus type 2 expressed fiber protein, whereas infected monkey cells alone did not. Hybrids constructed after the parental monkey cells were infected with adenovirus type 2 demonstrated that fiber synthesis in these cells could be rescued by fusion to uninfected human cells. Thus, human cells contain a dominant factor that acts in trans and overcomes the inability of monkey cells to synthesize fiber. Cells reconstructed from infected human karyoplasts and monkey cytoplasts expressed fiber, whereas cells reconstructed from infected monkey karyoplasts and human cytoplasts did not. These results are consistent with the hypothesis that the block to adenovirus replication in monkey cells involves a nuclear event that prevents the formation of functional mRNA for some late viral proteins including fiber polypeptide. Furthermore, they suggest that the translational apparatus of monkey cells is competent to translate functional fiber mRNA synthesized in human cells.

Subgenomic viral DNA species synthesized in simian cells by human and simian adenoviruses

DNA synthesized after infection of simian tissue culture cells (BSC-1 or CV-1) with human adenovirus type 2 or 5 or with simian adenovirus 7 was characterized. It was demonstrated that as much as 40% of the virus-specific DNA in nuclei of infected monkey cells consists of subgenomic pieces. No subgenomic viral DNA species were detected in the nuclei of human (HeLa) cells infected with these adenovirus types. Restriction analysis showed that these short viral DNA molecules contain normal amounts of the sequences from the ends of the viral genome, whereas internal regions are underrepresented. The production of subgenomic DNAs is not correlated with semipermissive infection. Although adenovirus types 2 and 5 are restricted in monkey cells, these cells are fully permissive for simian adenovirus 7. HR404, an adenovirus type 5 mutant which is not restricted in monkey cells, produced the same percentage of subgenomic DNAs as did its wild type (restricted) parent, and coinfection of monkey cells with adenovirus type 5 DNAs. The array of predominant size classes among the heterogeneously sized short DNAs is serotype specific. Extensive plaque purification and comparison of wild-type adenovirus type 5 with several viral mutants indicated that the distribution of aberrant sizes of DNA is characteristic of the virus and not a result of random replicative errors and then enrichment of particular species.

DNA replication and the early to late transition in adenovirus infection

Expression of the late genes of adenovirus is only detectable after virus DNA synthesis has occurred. Using a superinfection protocol, we show that replication of the template per se is required for expression of late regions L2--L5 (mapping to the right of position 39) and that the accumulation of early gene products does not suffice. This regulation is probably exerted at the level of transcription rather than by control of processing or selective stabilization of late mRNA or its precursors. The promoter-proximal late gene block L1, however, appears to be subject to processing control. At early times a single member of this gene family (tripartite leader plus coordinates 29--39, encoding the 52,55K polypeptide pair) is expressed, whereas at late times an additional, differently spliced mRNA species is generated from this region (tripartite leader plus coordinates 34--39, encoding polypeptide IIIa).

Expression of unselected adenovirus genes in human cells co-transformed with the HSV-1 tk gene and adenovirus 2 DNA

We have introduced adenovirus 2 genes into high molecular weight DNA of permissive human cells by co-transformation of tk- human 143 cells with Ad2 restriction enzyme fragments and a cloned Bam HI fragment that carries the HSV-1 thymidine kinase gene. Tk+ cells were isolated after selection and maintenance in HAT medium. Several co-transformed lines are able to complement the growth of Ad5 dl312 (delta 1.2--3.7) and Ad5 dl434 (delta 2.6--8.7), deletion mutants that lack sequences from the left end of the viral genome. The amount and arrangement of viral sequences in the co-transformed cell lines have been analyzed by restriction endonuclease digestion and filter hybridization. Most of the cell lines contain a single insertion of the HSV-1 tk fragment and a single insert of adenoviral DNA. However, one line (B1) contains at least four different insertions, two of which are present in multiple copies. The adenoviral DNA in all cell lines is composed of sequences from the left end of the genome and extends for varying lengths in different lines. Two cell lines that complement deletion mutants efficiently synthesize both early region 1a and 1b mRNAs. The B1 line synthesizes low levels of 1a mRNA, higher levels of 1b mRNA and a unique mRNA that maps to the right of the 1b gene family. When grown continuously in HAT medium, some cell lines are quite stable while others are fairly unstable. Some tk+ subclones support the growth of viral mutants as well as the parental line while others give reduced levels of complementation. For all tk+ subclones examined, the alteration or reduction in viral gene expression is independent of changes in the pattern of integration of viral DNA.

Adenovirus helper function for growth of adeno-associated virus: effect of temperature-sensitive mutations in adenovirus early gene region 2

Adeno-associated virus (AAV) grows efficiently only in cells that are also infected with an adenovirus (Ad). We employed Ad mutants to determine which genes may be required for the AAV helper function. Two mutants of Ad type 5 (Ad5), Ad5ts125 and Ad5ts107, with temperature-sensitive lesions in the E72 DNA-binding protein coded by the Ad early region 2, were deficient for AAV helper functions at the nonpermissive temperature (40 degrees C). In contrast, Ad5ts149, with a temperature-sensitive lesion in the Ad early region 5, was an efficient helper of AAV at the nonpermissive temperature. In KB cells, with the Ad5ts125 or Ad5ts107 mutant as the helper, the accumulation of AAV capsid proteins and AAV particles was decreased by about two logs, whereas AAV DNA synthesis was decreased only severalfold. Cytoplasmic, polyadenylic acid-containing AAV RNA is composed of a set of overlapping, spliced RNAs having different 5' start points. With the ts125 helper at 40 degrees C there was a decreased accumulation of some but not all of these AAV RNAs. The Ad5 E72 protein may have an effect on transcription or more likely posttranscriptional processing of AAV RNA. These observations suggest additional pleiotropic effects of the multifunctional E72 protein and suggest further similarities in the actions of E72 and the simian virus 40 T-antigen.

Nucleotide sequence of simian virus 40 DNA: structure of the middle segment of the HindII + III restriction fragment B (sixth part of the T antigen gene) and codon usage

We report here the nucleotide sequence of the simian virus 40 DNA region that lies between the EcoRII restriction endonuclease cleavage sites at map positions 0.214 and 0.281. The sequence was determined by partial chemical degradation of terminally labeled DNA fragments according to the procedure of Maxam and Gilbert. This region represents 6.7% of the SV40 genome and is located in the middle of HindII + III restriction fragment B. It is expressed as part of the early 19-S messenger RNA, which codes for the large-T antigen protein. Only one open reading frame for translation can be deduced from the message strand of the DNA and this reading frame connects in phase with the one of both neighboring fragments. This publication is the last in a series of papers about the T-antigen gene, and several properties of this gene and its product are discussed. The non-randomness of codon usage is similar to that previously discussed for the late part of the genome. Moreover, it appears that the choice of a third letter can be determined by the nature of the following codon; some codons which start with a pyrimidine are almost never preceded by an adenosine and some ANN-type codons are almost never preceded by a guanosine.

Simian virus 40 mutants with deletions at the 3' end of the early region are defective in adenovirus helper function

Coinfection of monkey cells with simian virus 40 (SV40) and adenovirus type 2 (Ad2) increased the Ad2 yield 1,000-fold over that obtained by Ad2 infection alone of monkey cells (A. S. Rabson, G. T. O'Conor, I. K. Berezesky, and F. J. Paul, Proc. Soc. Exp. Biol. Med. 116:187-190, 1964). The ability of viable mutants of SV40 that contain deletions at various sites in the viral DNA to enhance Ad2 growth in monkey cells was examined. Only those mutants with deletions near the 3' end of the early region were deficient in providing this helper function. Mutants dl1265, lacking 39 base pairs at map position 0.18, and dl1263, lacking 33 base pairs at map position 0.20 (H. van Heuverswyn, C. Cole, P. Berg, and W. Fiers, J. Virol. 30:936-941, 1979), were approximately 4 and 30% as effective as wild-type SV40, respectively. The extent of enhancement of Ad2 yield depended on the multiplicity of infection by SV40, but not by Ad2 (at a multiplicity of infection of </=50), as well as on the relative times of infection by Ad2 and SV40. Increasing the SV40 multiplicity of infection or infecting cells with SV40 wild type or mutants prior to Ad2 infection increased the Ad2 yield dramatically. The T antigens of wild-type SV40, dl1263, and dl1265 were examined. We attempt to correlate defects in helper function, alterations in the T antigen structure, and the DNA sequence of the mutants as determined by van Heuverswyn et al. (J. Virol. 30:936-941, 1979).

Characterization of a fused protein specified by the adenovirus type 2-simian virus 40 hybrid Ad2+ND1 dp2

The adenovirus type 2-simian virus 40 (SV40) hybrid virus Ad2+ND1 dp2 (E. Lukanidin, manuscript in preparation) specified two proteins (molecular weights, 24,000 and 23,000) that are, in part, products of an insertion of SV40 early DNA sequences. This was demonstrated by translation in vitro from viral mRNA that had been selected by hybridization to SV40 DNA. These two phosphorylated, nonvirion proteins were produced late in infection in amounts similar to adenovirus 2 structural proteins and were closely related to each other in tryptic peptide composition. The portion of SV40 DNA (map units 0.17 to 0.22 on the SV40 genome) coding for these proteins was joined to sequences coding for the amino-terminal part of the adenovirus type 2 structural protein IV (fiber). The Ad2+ND1 dp2 23,000- and 24,000-molecular-weight proteins were hybrid polypeptides, with about two-thirds of their tryptic peptides contributed by the fiber protein and the remainder contributed by SV40 T-antigen. They shared with T-antigen (molecular weight, 96,000) a carboxy-terminal proline-rich tryptic peptide. Together, the tryptic peptide composition of these proteins and the known SV40 DNA sequences suggested the reading frame for the translation of T-antigen. The carboxy terminus for T-anigen would then be located on the SV40 genome map next to the TAA terminator triplet at position 0.175, 910 bases away from the cleavage site of the restriction endonuclease EcoRI. Seven host range mutants from Ad2+ND1 dp2 were isolated that had lost the capacity to propagate on monkey cells. They did not induce detectable levels of the hybrid proteins. Three of these mutants had lost the SV40 DNA insertion that codes in part for these proteins. Thus, in analogy to the Ad2+ND1 30,000-molecular-weight protein, the presence of these proteins correlates with the presence of the helper function for adenovirus replication on monkey cells.

Characterization of a variant of human adenovirus type 2 which multiples efficiently in simian cells

In a previous report (Klessig, J. Virol. 21:1243--1246, 1977), the isolation of a variant (H2hr400) of adenovirus serotype 2 (Ad2) that overcomes the block to multiplication of wild-type Ad2 in simian cells was described. H2hr400 replicates efficiently on both human and simian cells, resulting in virus yields that are comparable to those found when wild-type Ad2 infects permissive, human cells. An extensive comparison of the genome of H2hr400 with that of its parent by restriction endonuclease, electron microscopic, and hybridization analyses failed to detect any differences and excludes the possibility that simian virus 40 sequences, which in certain Ad2-simian virus 40 hybrid viruses (e.g., Ad2+ND1) allow adenovirus to multiply efficiently in simian cells, are present in H2hr400. In contrast to Ad2, H2hr400 can fully express its late genes in both simian and human cells. The mutation has been mapped by a modified marker rescue technique to the segment of the viral genome located between coordinates 59 and 80.

Biosynthesis, immunological specificity, and intracellular distribution of the simian virus 40-specific protein induced by the nondefective hybrid Ad2+ND1

Ad2(+)ND(1), a nondefective hybrid virus containing a segment of the early region of simian virus 40 (SV40) DNA covalently inserted into the human adenovirus 2 genome, enhances the growth of human adenoviruses in simian cells and induces the SV40 U antigen. This hybrid previously has been shown to code for a 28,000 (28K) molecular weight protein not present in wild-type adenovirus 2-infected cells. By radioimmunoprecipitation using sera from hamsters bearing SV40-specific tumors, we have established that the Ad2(+)ND(1)-induced 28K protein is SV40-specific. This Ad2(+)ND(1)-induced protein is synthesized as a 30K molecular weight precursor, which is detectable only when infected cells are pulse-labeled in the presence of the protease inhibitor tosylamino phenylethyl chloromethyl ketone. Upon fractionation of labeled cell extracts, about 80% of the 28K protein is found in the plasma membrane fraction, whereas the remaining 20% is associated with the outer nuclear membrane. This protein is not detectable either in the nucleus or in the cytoplasm. Blockage of proteolytic cleavage by tosylamino phenylethyl chloromethyl ketone did not alter the topographic distribution of this SV40-specific protein, although the amount of the precursor protein in the outer nuclear membrane increased fourfold while that in the plasma membrane was proportionately decreased. This result suggests that the 28K protein is transferred from the outer nuclear membrane to the plasma membrane after posttranslational cleavage of the 30K precursor polypeptide. These data offer further support to the proposal that the 28K protein contains the determinants for SV40 U antigen and is responsible for SV40 enhancement of adenovirus growth in simian cells.

Biological activity of purified simian virus 40 T antigen proteins

Proteins related to simian virus 40 (SV40) T antigen uere isolated from cells infected with adenovirus 2/SV40 hybrids Ad2+D2 and Ad2+ND1 dp2 as well as from a line of human cells (SV80) transformed by SV40. The 96,000- and 107,000-dalton proteins of SV80 and Ad2+D2, after injection into the cytoplasm of cultured cells, rapidly accumulate in the nuclei, where they remain antigenically reactive for at least 20 hr and trigger DNA synthesis in quiescent cells. By contrast, the 23,000-dalton protein coded by Ad2+ND1 dp2 does not stimulate cellular DNA synthesis. However, all three purified proteins are able to provide helper function for the growth of adenovirus 2 in monkey cells. Thus, purified SV40 T antigen and proteins that share sequences with it retain the ability to carry out at least two functions associated with the product of the A gene of SV40.