Studies of nondefective adenovirus 2-simian virus 40 hybrid viruses. V. Isolation of additional hybrids which differ in their simian virus 40-specific biological properties

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.

Splicing in adenovirus and other animal viruses

Splicing provides viruses with great genetic versatility. It is still too early to say whether this versatility is derived from ingeneous mechanisms evolved by necessity by the viruses, or whether the viruses indeed mimic cellular mechanisms. In any event, it is unlikely that cells will provide a single genomic cluster of genes that utilize splicing in such diverse ways as adenovirus, or the other viruses discussed here. And we may speculate that when the full role of splicing in adenovirus gene expression program is known, its import will continue to be a source of amazement!

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.

Altered mRNA splicing in monkey cells abortively infected with human adenovirus may be responsible for inefficient synthesis of the virion fiber polypeptide

Messenger RNA encoding the fiber protein of the human adenovirus serotype 2 (Ad2) capsid is inefficiently translated in abortively infected African green monkey kidney cells. The amount of fiber mRNA present in the cytoplasm of abortively infected monkey cells is less than that in productively infected cells by a factor of 5-10 but synthesis of the fiber polypeptide is reduced by a factor of more than 100. Evidence from a variety of experiments indicates that the defect does not lie in the translational apparatus of the monkey cell but may best be explained by differences in the fiber messages made in abortively versus productively infected cells. Here we report that fiber mRNA isolated from abortively infected monkey cells is processed differently than that made in productively infected cells. Primer extension analysis of the 5' ends of fiber messages from several different productive and abortive infections shows a direct correlation between synthesis of the fiber polypeptide in vivo and the presence of the "x" and/or "y" ancillary leaders on messages encoding the fiber polypeptide. Of all the mRNAs encoded by the major late transcriptional unit of Ad2 only the fiber message can contain the x and y leaders, and the fiber protein is the only late Ad2 protein reported to be glycosylated. We speculate that these leader sequences play a role in the synthesis of this glycoprotein, as well as that of the Ad2 19-kilodalton glycoprotein encoded by early region 3, whose mRNA also contains the x and y leaders.

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.

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.

The adenovirus type 2-simian virus 40 hybrid virus Ad2+ND4 requires deletion variants to grow in monkey cells

The Ad2+ND4 virus is an adenovirus type 2 (Ad2)-simian virus 40 (SV40) recombination. The Ad2 genome of this recombinant has a rearrangement within early region 3; Ad2 DNA sequences between map positions 81.3 and 85.5 have been deleted, and the SV40 DNA sequences between map positions 0.11 and 0.626 have been inserted into the deletion in an 81.3-0.626 orientation. Nonhybrid Ad2 is defective in monkey cells; however, the Ad2+ND4 virus can replicate in monkey cells due to the expression of the SV40-enhancing function encoded by the DNA insert. Stocks of the Ad2+ND4 hybrid were produced in primary monkey cells by using the progeny of a three-step plaque purification procedure and were considered to be homogeneous populations of Ad2+ND4 virions because they induced plaques in primary monkey cells by first-order kinetics. By studying the kinetics of plaque induction in continuous lines (BSC-1 and CV-1) of monkey cells, we have found that stocks (prepared with virions before and after plaque purification) of Ad2+ND4 are actually heterogeneous populations of Ad2+ND4 virions and Ad2+ND4 deletion variants that lack SV40 and frequently Ad2 DNA sequences at the left Ad2-SV40 junction. Due to the defectiveness of the Ad2+ND4 virus, the production of progeny in BSC-1 and CV-1 cells requires complementation between the Ad2+ND4 genome and the genome of an Ad2+ND4 deletion variant. Since the deletion variants that have been obtained from Ad2+ND4 stocks do not express the SV40-enhancing function in that they cannot produce progeny in monkey cells, we conclude that they are providing an Ad2 component that is essential for the production of Ad2+ND4 progeny. These data imply that the Ad2+ND4 virus is incapable of replicating in singly infected primary monkey cells without generating deletion variants that are missing various amounts of DNA around the left Ad2-SV40 junction in the hybrid genome. As the deletion variants that arise from the Ad2+ND4 virus are created by nonhomologous DNA recombination, the generation of deletion variants in monkey cells infected with Ad2+ND4 may be a useful model for studying this process.

Aberrant distribution of human adenovirus type 2 late proteins in monkey kidney cells

Monkey kidney cells (CV-C) infected with adenovirus type 2 displayed an aberrant distribution of 100K, 100K-hexon complex, hexon monomers, hexon trimers, penton base, and fiber proteins, relative to the patterns observed in adenovirus type 2-infected human cells. Human cell patterns were observed in CV-C cells when mutants selected for growth on monkey cells were used.

An amber suppressor tRNA gene derived by site-specific mutagenesis: cloning and function in mammalian cells

We describe the synthesis, cloning, expression, and in vivo function of a suppressor tRNA gene in mammalian cells. By using "primer-directed mutagenesis" on a Xenopus laevis tyrosine tRNA gene cloned into the recombinant single-strand phage M13mp5, we have generated an amber suppressor tRNA gene that has a nucleotide change--GTA leads to CTA--in the anticodon sequence. The suppressor (Su) tRNA gene was introduced into monkey kidney cells (CV-1) by using simian virus 40 (SV40) DNA as vector (SV40-tRNATyrSu+). CV-1 cells infected with virus containing the mutant, but not the wild-type, tRNA gene produce a functional amber suppressor tRNA as indicated by suppression of amber mutations in co-infecting adenovirus serotype 2-SV40 hybrids. Further evidence that suppression of these amber mutations is tRNA mediated was derived by isolation of total tRNA from CV-1 cells infected with the SV40-tRNATyr (Su+) recombinant and its use in demonstration of read through of an amber codon during in vitro translation of tobacco mosaic virus RNA in reticulocyte extracts. Interestingly, the amplification of an amber suppressor gene in CV-1 cells does not interfere with SV40 production, suggesting that suppression of amber codons may not be very deleterious to mammalian cell metabolism.

Construction and characterization of viable deletion mutants of simian virus 40 lacking sequences near the 3' end of the early region

Five viable deletion mutants of simian virus 40 (SV40) were prepared and characterized. These mutants lack 15 to 60 base pairs between map positions 0.198 and 0.218, near the 3' end of the early region of SV40 and extend further into the body of the A gene, encoding the large T antigen, than previously described deletion mutants. These mutants were isolated after transfection of monkey kidney CV-1p cells with full-sized linear DNA prepared by partial digestion of form I SV40 DNA with restriction endonucleases HinfI or MboII, followed by removal of approximately 25 base pairs of DNA from the 5' termini using lambda-5'-exonuclease and purification of the DNA in agarose gels. Based on camparisons of the DNA sequence of SV40 and polyoma virus, these mutations map in the 19% of the SV40 A gene that shares no homology with the A gene of polyoma virus. The mutations exist in two different genetic backgrounds: the original set of mutants (dl2401 through dl2405) was prepared, using as a parent SV40 mutant dl862, which has a deletion at the single HpaII site (0.725 map unit). A second set (dl2491 through dl2495) contains the same deletions in a wild-type SV40 (strain SV-S) background. Relative to wild-type SV40, the original mutants showed reduced rates of growth, lower yields of progeny virus and viral DNA, and smaller plaque size; in these properties the mutants resembled parental dl862, although mutant progeny yields were usually lower than yields of dl862, suggesting a possible interaction between the two deletions. The second set of mutants had growth properties and progeny yields similar to those of wild-type SV40; however, Southern blotting experiments indicated that viral DNA replication proceeds at a slightly reduced rate. All of the mutants transformed mouse NIH/3T3 cells and mouse embryo fibroblasts at the same frequency as wild-type SV40. Mutants dl2402, dl2492, and dl2405 consistently produced denser and larger foci in both types of cells. All mutants directed the synthesis of shortened large T antigens. Adenovirus helper function was retained by all mutants.

Stimulation of host centriolar antigen in TC7 cells by simian virus 40: requirement for RNA and protein syntheses and an intact simian virus 40 small-t gene function

Simian virus 40 (SV 40) stimulated a host cell antigen in the centriolar region after infection of African green monkey kidney (AGMK) cells. The addition of puromycin and actinomycin D to cells infected with SV40 within 5 h after infection inhibited the stimulation of the host cell antigen, indicating that de novo protein and RNA syntheses that occurred within the first 5 h after infection were essential for the stimulation. Early viable deletion mutants of SV40 with deletions mapping between 0.54 and 0.59 map units on the SV40 genome, dl2000, dl2001, dl2003, dl2004, dl2005, dl2006, and dl2007, did not stimulate the centriolar antigen above the level of uninfected cells. This indicated that an intact, functional small-t protein was essential for the SV40-mediated stimulation of the host cell antigen. Our studies, using cells infected with nondefective adenovirus-SV40 hybrid viruses that lack the small-t gene region of SV40 (Ad2+ND1, Ad2+ND2, Ad2+ND3, Ad2+ND4, and Ad2+ND5), revealed that the lack of small-t gene function of SV40 could be complemented by a gene function of the adenovirus-SV40 hybrid viruses for the centriolar antigen stimulation. Thus, adenovirus 2 has a gene(s) that is analogous to the small-t gene of SV40 for the stimulation of the host cell antigen in AGMK cells.

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.

Transforming genes and gene products of polyoma and SV40

The small DNA-containing viruses, SV40 and polyoma, transform cells in vitro and induce tumors in vivo. For both viruses two genes required for transformation have been found. The genes required for transformation are also involved in productive infection. Although the two viruses are similar in their effects on cells, the organization of the transforming genes and gene products is different. The purpose of this review is to compare what is known about the biology and the biochemistry of the early regions of the two viruses. The genetic and biochemical studies defining the sequences important for transformation will be reviewed. Then, the products of the transforming genes, called T antigens, will be discussed in detail. There is a substantial body of descriptive information on those products, and studies on the function of the T antigens have also begun.

Mutant carrying deletions in the two simian virus 40 early genes

We isolated a simian virus 40 mutant, dl2194, which carried deletions in both early genes. One deletion removed 234 base pairs in the 54/59 region within the small-t-antigen coding sequence and the large-T-antigen gene intron. The second deletion removed 57 base pairs at the C terminus of the large-T-antigen coding sequence (0.20 map unit). dl2194 was a viable mutant, it carried a normal helper function for adenovirus growth on monkey cells, and it displayed the transformation properties of a small-t-antigen-negative single mutant. Therefore, none of the known large-T-antigen functions seemed to be altered by the C-terminal deletion.

Genomic arrangement of an adenovirus-simian virus 40 hybrid virus, Ad2+ND4del

Ad2+ND4del is an adenovirus type 2-simian virus 40 hybrid virus nondefective for growth in human cells. The virus was first observed when stocks of Ad2+ND4, a hybrid isolated from primary monkey kidney cells, were propagated in human cells. This paper describes the DNA sequence at two sites of DNA recombination, the site of the left adenovirus type 2-simian virus 40 junction and the site of a deletion of internal simian virus 40 sequences. Since the deletion was observed when the virus was switched from monkey to human cells, an analysis of gene expression in the region of DNA rearrangement may prove useful for the elucidation of molecular events that accompany virus growth in different hosts.

Late nonstructural 100,000- and 33,000-dalton proteins of adenovirus type 2. I. Subcellular localization during the course of infection

We analyzed the subcellular locations of the late adenovirus type 2 nonstructural 100,000-dalton (100K) and 33K proteins in adenovirus type 2-infected HeLa cells both by biochemical cell fractionation and by immunofluorescence microscopy, using specific antisera against purified sodium dodecyl sulfate-denatured 100K and 33K polypeptides. Both methods showed that the 100K protein was present in the cytoplasm as well as in the nuclei of infected cells and that it accumulated in the nuclei during the course of infection. Phosphorylated 100K protein also was found both in the cytoplasm and in nuclei. However, the nuclear 100K protein pool was phosphorylated to a higher degree than the cytoplasmic pool. In all experiments the 33K protein, which also is a phosphoprotein, was present exclusively in the nuclei of infected cells. The 100K and 33K proteins were associated with different nuclear substructures; this was demonstrated serologically by an analysis of infected cells in which double color immunofluorescence microscopy was used. In these experiments antibodies against the 100K protein decorated different nuclear structures than antibodies against the 33K protein.

Phosphorylation patterns of tumour antigens in cells lytically infected or transformed by simian virus 40

The phosphorylation sites of simian virus 40 (SV40) large tumor (T) antigens have been analyzed by partial proteolysis peptide mapping and phosphoamino acid analysis of the resulting products. At least four sites were found to be phosphorylated. An amino-terminal part of the molecule contained both phosphoserine and phosphothreonine. One phosphothreonine residue was located in the proline-rich carboxy-terminal end of the molecule, either at position 701 or at position 708. The mutant dl 1265, which is defective in adenovirus helper function, lacked this phosphorylation site. In addition, the carboxy-terminal part of the molecule contained phosphoserine at a more central position. T-antigen-associated proteins of SV40-transformed cell (nonviral T; 51,000 to 55,000 daltons) also contained multiple phosphorylation sites involving at least two serine residues in mouse antigens and an additional threonine residue in rat, human, and monkey antigens. The latter residue and at least one phosphoserine residue were located near one terminus of the human NVT molecule. We did not find any evidence for phosphorylation of tyrosine residues in any of the multiple species of either large T or nonviral T molecules. Several forms of large T antigens were extracted from both SV40-transformed and SV40-infected permissive and nonpermissive cells, and their phosphorylation patterns were compared. No evidence was found for a different phosphorylation pattern of T antigen in transformed cells.

Transcription and RNA processing by the DNA tumour viruses

Messenger RNA synthesis by the DNA tumour viruses proceeds by a complex but versatile series of transcription and RNA processing steps. The major mechanistic features of this pathway are probably very similar to those used by the animal cell host itself. The viruses have, however, evolved intricate arrangements of protein coding sequences and sites for RNA initiation, polyadenylation and splicing which allow them to use their genetic information to maximum advantage.

New chimeric splice junction in adenovirus type 2-simian virus 40 hybrid viral mRNA

We have examined hybrid viral RNAs synthesized in both human and monkey cells infected by three nondefective adenovirus type 2 (Ad2)-simian virus 40 (SV40) hybrid viruses; Ad2+ND1, Ad2+ND2, and Ad2+ND4. Most of the hybrid viral RNA molecules appeared to be initiated within adenoviral sequences, but were polyadenylated on their 3' end at the early SV40 mRNA polyadenylation site. The Ad2+ND4 stock of virus was not homogeneous, but consisted of two principle populations of viral DNA. Both populations contained a segment of SV40 DNA extending from the SV40 map positions 0.63 to 0.11 in a left-to-right orientation at adenovirus map position 0.82. One population contained an intact SV40 segment, whereas the other (representing 80 to 85% of the population) has a 500-base pair deletion mapping from approximately 0.60 to 0.50 SV40 map units. This deletion encompassed the SV40 DNA segment which encodes the early SV40 splice sites. Cells infected by the mixed Ad2+ND4 population induced the synthesis of at least three major SV40 RNA species among the hybrid viral transcripts. The most abundant of these hybrid mRNA's appeared only late in the lytic cycle, after the onset of viral DNA replication. It contained an RNA splice junction which extended from a donor (5') nucleotide within the adenoviral RNA sequences to an acceptor (3') splice site within the early region of SV40 at 0.46 SV40 map units. This SV40 acceptor splice site was remarkable in that its use has not been detected in the spliced viral mRNA's of SV40-infected or -transformed cells.

Cell surface location of simian virus 40-specific proteins on HeLa cells infected with adenovirus type 2-simian virus 40 hybrid viruses Ad2+ND1 and Ad2+ND2

HeLa cells infected with the nondefective adenovirus type 2-simian virus 40 hybrid viruses Ad2+ND1 or Ad2+ND2 were analyzed for cell surface location of the SV40-specific hybrid virus proteins by indirect immunofluorescence microscopy. Two different batches of sera from SV40 tumor-bearing hamsters, serum from SV40 tumor-bearing mice, or two different antisera prepared against purified sodium dodecyl sulfate-denatured SV40 T-antigen, respectively, were used. All sera were shown to exhibit comparable T- and U-antibody titers and to specifically immunoprecipitate the SV40-specific proteins from cell extracts of Ad2+ND2-infected cells. Whereas analysis of living, hybrid virus-infected HeLa cells did not yield conclusive results, analysis of Formalin-fixed cells resulted in positive cell surface fluorescence with both Ad2+ND1- and Ad2+ND2-infected HeLa cells when antisera prepared against sodium dodecyl sulfate-denatured SV40 T-antigen were used as first antibody. In contrast, sera from SV40 tumor-bearing animals were not or only very weakly able to stain the surfaces of these cells. The fact that the tumor sera had comparable or even higher T- and U-antibody titers than the antisera against sodium dodecyl sulfate-denatured T-antigen but were not able to recognize SV40-specific proteins on the cell surface suggests that SV40 tumor-specific transplantation antigen may be an antigenic entity different from T- or U-antigen.

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).

Subcellular Localization of simian virus 40 large tumor antigen

The distribution of simian virus 40 large tumor antigen in subcellular fractions from simian virus 40-transformed hamster (H-50) and mouse (VLM) cells and from simian virus 40-infected monkey cells was determined. Solubilized [(35)S]-methionine- or (32)P(i)-labeled surface membrane and nuclear fractions were prepared, immunoprecipitated with hamster anti-T serum, and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Tumor antigen with an apparent molecular weight of approximately 96,000 was detected in both subcellular fractions. Minor components of approximately 68,000 and approximately 56,000 with anti-T reactivity which labeled with [(35)S]methionine were also detected in both fractions from H-50 cells, as were components of approximately 140,000 and approximately 56,000 from VLM cells. The 56,000 component appeared to be greatly reduced in (32)P(i)-labeled surface membrane fractions. Normal cells or cells transformed with a heterologous agent, such as polyoma virus or a chemical carcinogen, lacked immunoprecipitable tumor antigen. Cell fractionation was monitored by [(3)H]thymidine labeling, NADH-diaphorase activity, and Na(+)-K(+)-dependent ATPase activity. These analyses revealed only trace contamination of surface membranes by nuclei, extremely low levels of nuclear rupture during homogenization, and an approximate 10-fold enrichment of surface membrane. Reconstruction experiments demonstrated that soluble tumor antigen failed to associate or copurify with surface membranes during fractionation procedures. These results indicate the presence of a protein in the plasma membrane of cells transformed or infected by simian virus 40 that is immunologically indistinguishable from nuclear tumor antigen.

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.

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.

Identification of amber and ochre mutants of the human virus Ad2+ND1

Although human adenoviruses grow poorly in monkey cells, this defect can be overcome either by coinfection of cells with simian virus 40 (SV40) or by insertion of the relevant portion of the SV40 genome into the adenovirus genome to form an adenovirus-SV40 hybrid virus. The nondefective adenovirus-2-SV40 hybrid virus, Ad2+ND1, contains an insertion of 17% of the SV40 genome, which codes for at least part of a 30,000 dalton protein. A set of Ad2+ND1 host-range mutants that have lost the ability to grow in monkey cells and behave as point mutants fail to synthesize the 30,000 dalton ND1 protein. Translation in vitro of SV40-specific mRNA from mutant-infected cells produces unique short polypeptides instead of the 30,000 dalton protein. Here we show that this set of host-range mutants includes both ochre and amber nonsense mutations. When the SV40-specific mRNA from the host-range mutants is translated in vitro to produce the polypeptide fragments, yeast suppressor tRNA can partially restore synthesis of wild-type-size 30,000 dalton protein. By this assay, one mutant is ochre and two are amber.

Evidence for simian virus 40 (SV40) coding of SV40 T-antigen and the SV40-specific proteins in HeLa cells infected with nondefective adenovirus type 2-SV40 hybrid viruses

HeLa cells infected with the nondefective adenovirus 2 (Ad2)-simian virus 40 (SV40) hybrid viruses (Ad2(+)ND1, Ad2(+)ND2, Ad2(+)ND4, and Ad2(+)ND5) synthesize SV40-specific proteins ranging in size from 28,000 to 100,000 daltons. By analysis of their methionine-containing tryptic peptides, we demonstrated that all these proteins shared common amino acid sequences. Most methionine-containing tryptic peptides derived from proteins of smaller size were contained within the proteins of larger size. Seventeen of the 21 methionine-containing tryptic peptides of the largest SV40-specific protein (100,000 daltons) from Ad2(+)ND4-infected cells were identical to methionine-containing peptides of SV40 T-antigen immunoprecipitated from extracts of SV40-infected cells. All of the methionine-containing tryptic peptides of the Ad2(+)ND4 100,000-dalton protein were found in SV40 T-antigen immunoprecipitated from SV40-transformed cells. All SV40-specific proteins observed in vivo could be synthesized in vitro using the wheat germ cell-free system and SV40-specific RNA from hybrid virus-infected cells that was purified by hybridization to SV40 DNA. As proof of identity, the in vitro products were shown to have methionine-containing tryptic peptides identical to those of their in vivo counterparts. Based on the extensive overlap in amino acid sequence between the SV40-specific proteins from hybrid virus-infected cells and SV40 T-antigen from SV40-infected and -transformed cells, we conclude that at least the major portion of the SV40-specific proteins cannot be Ad2 coded. From the in vitro synthesis experiments with SV40-selected RNA, we further conclude that the SV40-specific proteins must be SV40 coded and not host coded. Since SV40 T-antigen is related to the SV40-specific proteins, it must also be SV40 coded.

Simian virus 40-specific ribosome-binding proteins induced by a nondefective adenovirus 2-simian virus 40 hybrid

We have studied the intracellular distribution of the two simian virus 40-specific proteins, with apparent molecular weights of 56,000 and 42,000, detectable in human KB cells infected by a nondefective adenovirus 2-simian virus 40 hybrid, Ad2+ND2. After a 20-min pulse of [35S]methionine, about two-thirds of the newly synthesized 56K protein and one-third of the 42K protein were found localized on the plasma membrane. The remainder of each protein was found in the cytoplasm, whereas the nuclear fraction was virtually free of either component. A significant portion of both proteins present in the cytoplasmic fraction was complexed to the 40S ribosomal subunits and was not removed by treatment with 0.5 M KCl. Moreover, the portion that was found free in the cytoplasm could bind preferentially and quantitatively to purified 40S ribosomes in vitro, leading us to propose that these simian virus 40 proteins may act as translational control elements in cells.

Stimulation of RNA synthesis in isolated nuclei by partially purified preparations of simian virus 40 T-antigen

T-Antigen was partially purified from nuclei of cells transformed by simian virus 40 (SV 40). When nuclei isolated from either rat liver or quiescent hamster cells were preincubated with T-antigen preparations, there was a marked stimulation of RNA synthesis in an in vitro assay, up to 150% above control levels. The stimulation of RNA synthesis was inhibited by hamster antiserum against T-antigen but not by normal hamster serum. When the T-antigen preparations were fractionated on glycerol gradients, the fractions containing complement-fixing activity with antiserum to T-antigen also had the highest stimulatory activity on nuclear RNA synthesis. T-Antigen was also partially purified from nuclei of cells transformed by a temperature-sensitive A mutant of SV40. When preincubated up to 2 hr at 50 degrees, the T-antigen preparation from these temperature-sensitive A mutants was rapidly inactivated, in terms of both complement-fixing activity and ability to stimulate RNA synthesis in isolated rat liver nuclei. Under the same conditions of preincubation, T-antigen preparations from cells transformed by wild-type SV40 maintained their complement-fixing activity and ability to stimulate RNA synthesis. These results suggest that the biological action of T-antigen may be exerted at the level of transcription.

Specificity of initiation of transcription of simian virus 40 DNA I by Escherichia coli RNA polymerase: identification and localization of five sites for initiation with [gamma-32P]ATP

Simian virus 40 (SV40) DNA I was transcribed with Escherichia coli RNA polymerase in the presence of gamma-32P-labeled ribonucleoside triphosphates in order to investigate the specificity of initiation of in vitro transcription. ATP and GTP served as predominant initiating nucleotides, the former being incorporated about twice as much as the latter. Cleavage of [gamma-32P]ATP-labeled SV40 complementary RNA (cRNA) with T1 RNase followed by homochromatographic analysis of the resultant 5' initiation fragments revealed the presence of four specific initiation fragments 6 to 9 nucleotides in length, designated AI, AII, AIIIa, and AIIIb. By means of hybridization of [gamma-32P]ATP-labeled SV40 cRNA to DNA from specific adenovirus 2-SV40 hybrids and specific restriction endonuclease fragments of SV40 DNA before chromatographic analysis, it was possible to identify and determine approximate localizations of five [gamma-32P]ATP initiation sites on the SV40 genome: one in Hin-G close to the Hin-G-B junction, giving rise to the AII fragment, two in the overalpping fragment Hin-A-Hae-A,giving rise to AI and AIII fragments, and two in the fragment Hin-A-Hae-E, also giving rise to AI and AIII fragments. All five sites either fall within or lie near regions of the genome that are cleaved by S1 nuclease and subject to partial alkaline denaturation. These five sites lie on the minus strand of SV40 DNA and initiate RNAs that are copied in a leftward direction. Cleavage of [gamma-32P]GTP-labeled cRNA with pancreatic RNase liberated three major 5' initiation fragments of short length, GI, GII, and GIII, suggesting the presence of three principal GTP initiation sites.