Identification of simian virus 40 tumor and U antigens

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.

Stimulation of DNA polymerase alpha by a nuclear DNA/protein complex

A nuclear DNA complex containing DNA polymerase and SV40 T-antigen was isolated from nuclei of SV40-transformed mouse fibroblasts. DNA polymerase could be separated from the complex. The remaining DNA/T-antigen-containing complex stimulated DNA polymerase alpha activity about 10-fold. The complex contained 4 major proteins with molecular weights of 46, 54, 76, and 94 kilo-dalton (KD). The stimulation activity was retained by protein A-Sepharose loaded with specific IgG from SV40-tumor bearer serum, or from antisera against the 94 KD and 76 KD components and was partially inhibited in the presence of these antisera. The stimulation activity was completely abolished by treatment of the complex with trypsin or DNase I.

Monoclonal antibodies against simian virus 40 tumor antigens: analysis of antigenic binding sites, using adenovirus type 2-simian virus 40 hybrid viruses

The antigenic binding sites of two monoclonal antibodies are located in the COOH-terminal region (clone 412) and probably in an internal region (clone 7) of simian virus 40 large T antigen. A third monoclonal antibody (clone 122), which has been shown to bind nonviral T antigen, does not react with HeLa cells infected with nondefective adenovirus type 2 (Ad2)-simian virus 40 hybrid viruses Ad2+ND1, Ad2+ND2, or Ad2+ND4.

Association of simian virus 40 T antigen with replicating nucleoprotein complexes of simian virus 40

An immunoprecipitation assay was established for simian virus 40 T-antigen-bound nucleoprotein complexes by means of precipitation with sera from hamsters bearing simian virus 40-induced tumors. About 80% of simian virus 40 replicating nucleoprotein complexes in various stages of replication were immunoprecipitated. In contrast, less than 21% of mature nucleoprotein complexes were immunoprecipitated. Pulse-chase experiments showed that T antigen was lost from most of the nucleoprotein complexes concurrently with completion of DNA replication. T antigen induced by dl-940, a mutant with a deletion in the region coding for small T antigen, was also associated with most of the replicating nucleoprotein complexes. Once bound with replicating nucleoprotein complexes at the permissive temperature, thermolabile T antigen induced by tsA900 remained associated with the complexes during elongation of the replicating DNA chain at the restrictive temperature. These results suggest that simian virus 40 T antigen (probably large T antigen) associates with nucleoprotein complexes at or before initiation of DNA replication and that the majority of the T antigen dissociates from the nucleoprotein complexes simultaneously with completion of DNA replication.

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.

Nucleotide sequence of the simian virus 40 HindII + III restriction fragment I (fourth part of the T antigen gene)

The HindII + III restriction fragment I (Hind-I) from simian virus 40 DNA represents 4.96% of the genome and maps in the early transcription region. Hind-I is an internal segment of the A gene and its information is expressed as part of the early 19-S mRNA, which codes for T antigen. We report here the nucleotide sequence of the 259-base-pair Hind-I fragment. The sequence was determined and confirmed by RNA and DNA sequencing methods: by analysis of oligonucleotides resulting from T1 and pancreatic RNase digestion of labeled RNA transcribed from SV40 DNA with Escherichia coli DNA-dependent RNA polymerase, by partial degradation of RNA transcripts with snake venom phosphodiesterase, and by base-specific chemical degradation of 5'-end-labeled subfragments of Hind-I according to the procedure of Maxam and Gilbert. Multiple triplets corresponding to termination codons occur in two of the three reading frames of the DNA strand that has the same polarity as early mRNA. The open reading frame connects in phase with the one of the Hind fragments flanking Hind-I, and the amino acid sequence specified by Hind-I lies in the middle part of the large-T antigen. Some features of the primary nucleotide sequence and of early transcription are discussed.

Pathogenic murine coronaviruses. II. Characterization of virus-specific proteins of murine coronaviruses JHMV and A59V

We have identified nine intracellular virus-specific proteins in cells infected with JHMV or A59V. Seven virus-specific proteins were detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and two additional virus-specific proteins were detected by two-dimensional gel electrophoresis. The A59V- and JHMV-specific proteins differ slightly in molecular weight. Four of the nine proteins are structural proteins. The synthesis of the nine virus-specific proteins is noncoordinate with respect to time.

Simian virus 40 T- and U-antigens: immunological characterization and localization in different nuclear subfractions of simian virus 40-transformed cells

Simian virus 40 (SV40)-transformed cells and cells infected by the nondefective adenovirus 2(Ad2)-SV40 hybrid viruses Ad2+ND1 and Ad2+ND2 were analyzed for SV40 T- and U-antigens, respectively, using individual hamster SV40 tumor sera or serum for which U-antibodies were removd by absorption. These studies showed that (i) T- and U-antigens can be defined by separate classes of antigenic determinants and (ii) the U-antigenic determinants in SV40-transformed cells and in hybrid virus-infected cells are similar. The apparent discrepancy in the subcellular location of U-antigen in SV40-transformed cells (nuclear location) and in hybrid virus-infected cells (perinuclear location) as determined by immunofluorescence staining of methanol/acetone-fixed cells could be resolved by treating hybrid virus-infected cells with a hypotonic KCl solution before fixation. Upon this treatment hybrid virus-infected cells also showed nuclear U-antigen staining. The possibility of an association of T- and U-antigens with different nuclear subfractions in SV40-transformed cells was investigated. Detergent-cleaned nuclei of SV40-transformed cells were fractionated into nuclear matrices and a DNase-treated, high-salt nuclear extract. Analysis of the nuclear matrices by immunofluorescence microscopy with T+U+ and T+U- hamster SV40 tumor serum revealed that U-antigen remained associated with the nuclear matrices, whereas T-antigen could not be detected in this nuclear subfraction. T-antigen, however, could be immunoprecipitated from nuclear extracts of the SV40-transformed cells.

Extraction and fingerprint analysis of simian virus 40 large and small T-antigens

A study of simian virus 40 (SV40) T-antigens isolated from productively infected CV1 cells using a variety of different extraction procedures showed that under some conditions the highest molecular weight form of T-Ag (large-T) isolated comigrated on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with large-T from SV40-transformed H65-90B cells. Other faster-migrating forms of large-T are probably generated during the extraction procedure by a protease which is active at low pH, and such forms are probably experimental artifacts. After extraction under conditions which minimize proteolytic degradation of large-T, a further form of T-antigen was isolated; this has an apparent molecular weight in the range 15,000 to 20,000 and is referred to as small-t. Fingerprint analysis of [35S]methionine-labeled SV40 proteins showed that small-t has 10 to 12 methionine peptides whereas large-T has 15 to 18 methionine peptides. All but two of the methionine tryptic peptides present in small-t are also present in large-T. The fingerprint data also showed that T-antigens have no peptides in common with SV40 VP1. Experiments using reagents which inhibit posttranslational cleavage of encephalomyocarditis virus polyproteins showed that these reagents do not affect the synthesis of small-t and suggest that it is not made by proteolytic cleavage of large-T in vivo. An alternative model, which proposes that large-T and small-t are synthesized independently, is discussed in terms of the fingerprint data and the number of methionine tryptic peptides predicted from the primary sequence of SV40 DNA.

Tumor-specific transplantation antigen: use of the Ad2+ND1 hybrid virus to identify the protein responsible for simian virus 40 tumor rejection and its genetic origin

Cells transformed by simian virus 40 (SV40) possess a tumor-specific transplantation antigen (TSTA) that has the property of immunizing animals against syngeneic tumor challenge. We find that the early SV40 DNA segment present in the human adenovirus 2 (Ad2)-SV40 hybrid, Ad2+ND1, is sufficient to induce this SV40-specific TSTA in BALB/c mice. Moreover, studies on the intracellular distribution of TSTA activity in Ad2+ND1-infected cells, as determined by the ability of various subcellular fractions to immunize mice against syngeneic tumor challenge, have suggested a correlation between this biological activity and the presence of the SV40-specific 28,000Mr protein in coded by this hybrid virus. Both the TSTA activity and the 28,000 Mr protein are found in the plasma membrane fraction and in the perinuclear region of infected cells but are virtually undetectable in the cytoplasmic fraction. Using a hamster antitumor antiserum that can specifically immunoprecipitate the 28,000 Mr protein, we are able to demonstrate a loss of TSTA activity concomitant with the removal of this SV40-coded protein. Thus, it appears that antigenic determinants responsible for SV40-specific tumor rejection in mice are contained within the 28,000 Mr protein coded for by the early SV40 DNA segment that extends from 0.17 to 0.28 map unit.

Nucleotide sequence of the simian virus 40 small-t gene

The nucleotide sequence of the segment of simian virus 40 DNA between standard map positions 0.53 and 0.65, i.e., approximately half of the restriction fragment Hind A, is reported. This segment is located near the beginning of the early region and is transcribed counterclockwise. There is a potential initiating ATG signal at 13 nucleotides from the Hind C-Hind A junction in the strand with the same polarity as the early mRNA. From this signal on, an open reading frame is present which would allow the synthesis of a polypeptide of 174 amino acids until a TAA termination codon is reached at nucleotide 602 (map position 0.547). This polypeptide, revealed by the DNA sequence, corresponds almost certainly to small-t antigen. Correlation of the deduced amino acid sequence with the NH(2)-terminal sequences of small-t and large-T (tumor) antigens of simian virus 40, as established by Paucha et al. [Paucha, E., Mellor, A., Harvey, R., Smith, A. E., Hewick, R. M. & Waterfield, M. D. (1978) [Proc. Natl. Acad. Sci. USA 75, 2165-2169], strongly argues that both proteins are indeed initiated at the ATG triplet. Because the DNA region between 0.547 and 0.534 is blocked for translation in all three reading frames by multiple termination condons, we conclude that the large-T antigen must be coded for by two noncontiguous DNA segments: the segment from 0.65 to around 0.60, which small-t and large-T antigens share, and another segment starting at some point after position 0.534 and continuing counterclockwise until it terminates at map position 0.174. Small-t antigen is methionine-rich and has a remarkably high number of cysteine residues clustered mainly in its COOH-terminal half. It is rich in both basic and acidic residues, the former being slightly in excess.

Simian virus 40-specific proteins in the membranes of simian virus 40-transformed hamster and mouse cells

Membranes of simian virus 40-transformed hamster lymphocytes and phagocytes, as well as of transformed mouse fibroblasts, contain two classes of antigenic virus-specific protein. The isoelectric points of these proteins, as defined by isoelectric focusing/immune electrophoresis are at pH 4.5 and 4.7. The molecular weights of the pI 4.5 and pI 4.7 components, determined by isoelectric focusing/dodecyl sulfate polyacrylamide electrophoresis, lie near 58,000 and 90,000-110,000, respectively. The pI 4.5 and pI 4.7 proteins are tentatively identified with the surface (transplantation) and U antigens, respectively.

Virus-specific proteins in the plasma membrane of cells lytically infected or transformed by pol-oma virus

Antisera, raised in rats, containing specificities directed against tumor antigen of polyoma virus also react with several proteins present in the plasma membrane of mouse cells infected with the virus. The main component has an apparent molecular weight of 55,000. The appearance of this protein after infection with early temperature-sensitive A mutants was temperature-dependent like tumor antigen itself. Pulse and chase isotope experiments suggest that this protein originates from a precursor, perhaps by cleavage; its production appears to be facilitated by the A mutation. Two other components with apparent molecular weights of 61,000 and 28,000 were also present but were more variable from experiment to experiment. All proteins were absent from the plasma membranes of cells infected with a transformation-defective mutant, NG-18. Up to four virus-specific proteins could be isolated from the plasma membranes of rat, hamster, and mouse cells transformed by the virus. The possible role of the plasma membrane proteins in cell transformation is discussed.

Transformation by simian virus 40 induces virus-specific, related antigens in the surface membrane and nuclear envelope

Nucleus- and mitochondrion-free membranes from hamster lymphocytes transformed by simian virus 40 (SV40), GD248 cells, cause guinea pigs to produce immune sera that reveal the presence in GD248 plasma membranes and mitochondria of two types of glycoprotein that are not detected in membranes of normal lymphocytes [Schmidt-Ullrich, R., Thompson, W. S. & Wallach, D. F. H. (1977) Proc. Natl. Acad. Sci. USA 74, 643-647]. Indirect immune fluorescence of living, SV40-transformed T19 hamster reticulum cells, Balb/c 3T3 mouse fibroblasts, and W18 VA2 human fibroblasts, using the antisera against GD248 membrane, at 4 degrees produced a distinct cell surface fluorescence; however, above 20 degrees , staining at the nuclear perimeter, the SV40 U-antigen reaction, becomes equally prominent. In SV40-transformed cells that had been fixed in cold acetone, as well as in purified GD248 nuclei, thermostable U-antigen staining is dramatic, but there is no reaction for nuclear T-antigen. Rabbit antisera against T19 cells gave immunofluorescence reactions equivalent to those obtained with the antisera against GD248 cells. Normal guinea pig or rabbit sera and cells that had not been transformed by SV40 gave no reaction. Our sera from tumor-bearing hamsters gave only nuclear T-antigen fluorescence. The results indicate the presence of related, SV40-specific antigens in the surface membranes, nuclear envelope, and possibly other intracellular organelles of SV40-transformed cells.