Two forms of simian-virus-40-specific T-antigen in abortive and lytic infection

On the functional roles of simian virus 40 large and small T-antigen in the induction of a mitotic host response

The early gene of wild-type (wt) SV40 specifies two related proteins, referred to as large (Mr 88,000) and small (Mr 19,000) T-antigen. Infection with wt SV40 of Go/G1-arrested monkey kidney and CV-1 cell cultures induced in virtually 100% of the cells T-antigen synthesis, followed by a mitotic reaction and the production of SV40 DNA. Parallel cultures were infected with SV40 deletion mutants that produce either no small T-antigen (d1883) or only trace amounts of a truncated form (d1891). Kinetics of synthesis and accumulation of large T-antigen was closely similar to that observed with wtSV40 whereas apparently only 50-60% of the cells participated in the mitotic reaction and the production of viral DNA. These results and those obtained from a comparative study on the abortive (transforming) infection in Go-arrested mouse tissue culture cells indicate that synthesis of large T-antigen alone is sufficient to trigger in 50-60% of the infected cells a mitotic reaction.

Regulation of protein synthesis in virus-infected animal cells

This chapter summarizes the structural features that govern the translation of viral mRNAs: where the synthesis of a protein starts and ends, how many proteins can be produced from one mRNA, and how efficiently. It focuses on the interplay between viral and cellular mRNAs and the translational machinery. That interplay, together with the intrinsic structure of viral mRNAs, determines the patterns of translation in infected cells. It also points out some possibilities for translational regulation that can only be glimpsed at present, but are likely to come into focus in the future. The mechanism of selecting the initiation site for protein synthesis appears to follow a single formula. The translational machinery displays a certain flexibility that is exploited more frequently by viral than by cellular mRNAs. Although some of the parameters that determine efficiency have been identified, how efficiently a given mRNA will be translated cannot be predicted by summing the known parameters.

Binding sites for monoclonal antibodies and for mRNPs on SV40 large T-antigen determined with a cleavage map

Immune complexes of simian virus 40 large T-antigen with monoclonal papovavirus protein antibodies PAb 416, PAb 402, or PAb 423 were bound to protein-A-Sepharose and then cleaved into discrete fragments by limited tryptic proteolysis. PAb 402 protected a specific cleavage site, located approximately within amino acid residues 450-500, from tryptic proteolysis; PAb 423 protected another site within residues 675-699. As shown by immunoblotting, 125I-labeled PAb 416 was bound to a 17-kDa N-terminal fragment of large T-antigen (amino acid residues 1-130), and PAb 423 was bound to several overlapping fragments derived from the C terminus of large T-antigen. These monoclonal antibodies were then used as accessibility probes to study the interaction of mRNPs with cytoplasmic large T-antigen. Whereas small T-antigen and nuclear large T-antigen were fully immunoreactive, cytoplasmic large T-antigen reacted poorly with PAb 402 or polyclonal antibodies unless the mRNP moiety was removed by treatment with EDTA/RNase A. In contrast, mRNP/T-antigen complexes were fully immunoreactive with PAb 416 or PAb 423 and did not require treatment with EDTA/RNase A. The results suggest that the binding site of PAb 402 is blocked due to the interaction with mRNPs whereas the N-terminal binding site of PAb 416 and the C-terminal binding site of PAb 423 remain accessible to antibodies.

Acylated simian virus 40 large T-antigen: a new subclass associated with a detergent-resistant lamina of the plasma membrane

We have analyzed the plasma membrane association of the SV40 large tumor antigen (large T) in SV40-transformed BALB/c mouse tumor cells (mKSA). Isolated plasma membranes were subfractionated: treatment with the non-ionic detergent Nonidet P40 (NP40) resulted in a NP40-resistant plasma membrane lamina, which could be further extracted with the zwitterionic detergent Empigen BB. Analysis of the different plasma membrane fractions revealed that only about one third of large T associated with isolated plasma membranes could be solubilized with NP40. The residual plasma membrane-associated large T was tightly bound to the NP40-resistant lamina of the plasma membrane from which it was released by treatment with the zwitterionic detergent Empigen BB. Further evidence for a specific interaction of a distinct subclass of large T with the plasma membrane was provided by showing that only T associated with the NP40-resistant lamina of the plasma membrane contained covalently bound fatty acid. Neither nuclear large T nor large T in the NP40-soluble plasma membrane fraction could be labeled with [3H]palmitic acid. Our results indicate that an acylated subclass of large T interacts specifically with a structure of the plasma membrane, suggesting that it might be involved in a membrane-dependent biological function.

The relation between polyoma T-antigen and increased 5S RNA synthesis in cell-free extracts from polyoma-infected mouse kidney cell cultures

In polyoma-infected mouse kidney cell cultures 5S RNA synthesis began to increase around 16 h, i.e. 7-9 h after the onset of polyoma T-antigen synthesis. The rate of polyoma-induced 5S RNA synthesis reached a maximum plateau around 25 h when it was 1.8-2.0 times higher than in mock-infected parallel cultures. Stimulation of 5S RNA synthesis in vivo thus coincided in time with the increase in total cellular RNA and protein. Cell-free extracts (S100) prepared at 15 h from mock-(S100-M) or polyoma-infected (S100-Py) mouse kidney cell cultures were indistinguishable with respect to protein concentration and 5S RNA synthesis, using a cloned somatic Xenopus borealis 5S gene as template. S100-Py extracted 25 h after infection contained 30% more protein and synthesized 1.5-2.0 times more 5S RNA than S100-M. Complete removal of the polyoma T-antigens from S100-Py by 3 cycles of immunoprecipitation with hamster anti-T serum remained without effect on stimulated 5S RNA synthesis. However, a linear relationship between 5S RNA synthesis and protein concentration of S100-M and S100-Py was observed.

Messenger ribonucleoproteins of cells infected by simian virus 40 contain large T-antigen

In monkey or mouse cells undergoing lytic or transforming infection with simian virus 40, about 10% of large tumor antigen (T-antigen) molecules were consistently present in the cytoplasm and 90% in the nucleus. The bulk of cytoplasmic large T-antigen cosedimented in linear sucrose gradients with polyribosomes (150-500 S) and with messenger ribonucleoproteins sedimenting within 20-80 S. As determined by centrifugation in discontinuous sucrose gradients, its apparent density (1.2-1.3 g/ml) corresponded to that of ribonucleoproteins. In contrast, the bulk of nuclear T-antigen sedimented between 5-20 S and its apparent density (1.1 g/ml) corresponded to that of free protein. Nuclear T-antigen added before cell fractionation did not bind to cytoplasmic constituents. After dissociation of purified polyribosomes with puromycin/KCl or EDTA, cytoplasmic large T-antigen cosedimented with the released messenger ribonucleoproteins containing poly(A)-rich messenger RNA. Upon hydrolysis of the RNA with RNase A, large T-antigen exhibited the sedimentation properties and density of free protein. The results suggest that cytoplasmic large T-antigen is associated with messenger ribonucleoproteins.

Nonlytic simian virus 40-specific 100K phosphoprotein is associated with anchorage-independent growth in simian virus 40-transformed and revertant mouse cell lines

Normal fibroblasts display two distinct growth controls which can be assayed as requirements for serum or for anchorage. Interaction of mouse 3T3 fibroblasts with simian virus 40 (SV40) thus generates four classes of transformed cells. We have examined viral gene expression in these four classes of cell lines. Immunoprecipitation of [35S]methionine-labeled cell extracts with an antiserum obtained from tumor-bearing hamsters detected the SV40 large T and small t proteins (94,000 molecular weight [94K], 17K) and the nonviral host 54K protein in all cell lines tested. A tumor antigen with an apparent molecular weight of 100,000 was also found in some, but not all, lines. Similar "super T" molecules have been found by others in many rodent transformed lines. We carried out an analysis of the relation of phenotype to relative amounts of these proteins in cell lines of the four classes, using the Spearman rank correlation test. The amount of the 100K T antigen relative to the 94K T antigen or to total viral protein was well correlated with the ability to form colonies in semisolid medium. No significant correlation was found between quantities of labeled 94K T antigen, 54K host antigen, or 17K t antigen and either serum or anchorage independence. Mouse cells transformed with the small t SV40 deletion mutant 884 synthesized a 100K T antigen, suggesting that small t is not required for the production of this protein. The 100K T antigen migrated more slowly than lytic T. Since mixtures of extracts from cells expressing and lacking the 100K T antigen yielded the expected amount of this protein, it is unlikely that the 100K T derives from the 94K protein by a posttranslational modification.

Simian virus 40 large tumor antigen: a "RNA binding protein"?

Simian virus 40 large tumor antigen was isolated by immunoaffinity chromatography from monkey or mouse cell cultures undergoing lytic or transforming infection. RNase-treated gel-purified large tumor antigen, on hydrolysis with alkali, gave about equimolar amounts of AMP, GMP, CMP, and UMP. Furthermore, RNA fragments of approximately 45 nucleotides could be isolated from large tumor antigen purified by the same procedure. Mapping of the T1 oligonucleotides showed a high complexity, as indicated by the presence of unique sequences of 15-30 nucleotides and of poly(A). This is compatible with the hypothesis that these RNA fragments are derived from cellular pre-mRNAs or mRNAs. Our results suggest that Simian virus 40 large tumor antigen is a RNA-binding protein and might possibly be involved in regulation of synthesis, maturation, or translation of cellular mRNAs.

Detection of a complex of SV40 large tumor antigen and 53K cellular protein on the surface of SV40-transformed mouse cells

The possible interaction between simian virus 40 (SV40) large tumor antigen (T-ag) and cellular proteins in the plasma membrane of SV40-transformed mouse cells was investigated. The presence of SV40 T-ag, 53,000 (53K) cellular protein, and histocompatibility (H-2) antigens on the surface of SV40-transformed cells was demonstrated by immunofluorescence. The use of lactoperoxidase-catalyzed cell surface iodination and a differential immunoprecipitation technique established that large T-ag is associated with the 53K host-coded protein on the surface of the transformed cells. In contrast, no detergent-stable complex between large t-ag and H-2 antigens was detected. Both labeled T-ag and 53K protein were coprecipitated from surface-iodinated SV40-transformed cells by monoclonal antibodies directed against either the viral or the cellular protein. Based on the unique antigenic sites recognized by the anti-T monoclonal antibodies, it appears that both the carboxy and amino termini of the T-ag polypeptide are exposed on the surface of SV40-transformed mouse cells. The nature of the association between surface T-ag and 53K protein, as well as that between the molecular complex and the plasma membrane, remains to be determined. The possible effect of the surface-associated T-ag/53K complex on cellular proliferation is considered.

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.

Nonlytic simian virus 40-specific 100K phosphoprotein is associated with anchorage-independent growth in simian virus 40-transformed and revertant mouse cell lines

Normal fibroblasts display two distinct growth controls which can be assayed as requirements for serum or for anchorage. Interaction of mouse 3T3 fibroblasts with simian virus 40 (SV40) thus generates four classes of transformed cells. We have examined viral gene expression in these four classes of cell lines. Immunoprecipitation of [35S]methionine-labeled cell extracts with an antiserum obtained from tumor-bearing hamsters detected the SV40 large T and small t proteins (94,000 molecular weight [94K], 17K) and the nonviral host 54K protein in all cell lines tested. A tumor antigen with an apparent molecular weight of 100,000 was also found in some, but not all, lines. Similar "super T" molecules have been found by others in many rodent transformed lines. We carried out an analysis of the relation of phenotype to relative amounts of these proteins in cell lines of the four classes, using the Spearman rank correlation test. The amount of the 100K T antigen relative to the 94K T antigen or to total viral protein was well correlated with the ability to form colonies in semisolid medium. No significant correlation was found between quantities of labeled 94K T antigen, 54K host antigen, or 17K t antigen and either serum or anchorage independence. Mouse cells transformed with the small t SV40 deletion mutant 884 synthesized a 100K T antigen, suggesting that small t is not required for the production of this protein. The 100K T antigen migrated more slowly than lytic T. Since mixtures of extracts from cells expressing and lacking the 100K T antigen yielded the expected amount of this protein, it is unlikely that the 100K T derives from the 94K protein by a posttranslational modification.

Inducible permissive cells transformed by a temperature-sensitive polyoma virus: superinfection does not allow excision of the resident viral genome

After exposure of mouse embryo cells to the early temperature-sensitive mutant tsP155 of polyoma virus (Py), a transformed cell line (Cyp line) that can be readily induced to synthesize Py by transfer to 33 degrees C was isolated at 39 degrees C (7). Virus production and synthesis of free viral DNA occurring after temperature shiftdown or superinfection with wild-type Py or both were studied in several clonal isolates of the Cyp cell line. Measurements of virus yields indicated that, although some could be induced more effectively than others, all cell clones behaved as highly permissive when subjected to superinfection. We analyzed the origin of free viral DNA accumulating in the superinfected cultures, taking advantage of (i) the unique physical properties of the low-molecular-weight DNA which, in the case of one of the Cyp clones, accumulates during temperature shiftdown, and (ii) the differences between resident and superinfecting viral genomes in their susceptibilities towards restriction endonucleases. At 33 degrees C, both viral genomes were found to accumulate in all clones studied whereas in the case of the clones with lower inducibility, the replication of the resident genome appeared to be enhanced by superinfection. At 39 degrees C, however, accumulation of the superinfecting genome was not accompanied by that of the resident genome, unless it had already been initiated before superinfection. These findings demonstrate that, when routinely cultivated at 39 degrees C, Cyp cells contain few viral DNA molecules readily available for autonomous replication and that, upon transfer to 33 degrees C, therefore, excision must first take place before the resident genome can accumulate as free viral DNA. Our findings also suggest that, unlike the P155 gene product provided by the resident viral genome upon induction, the allelic gene product supplied by the superinfecting genome may be less effective in triggering excision than in promoting replication.

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.

Purification of herpes simplex virus tumor associated antigen from human kidney carcinoma

In the present study, we attempted to purify herpes simplex virus (HSV) tumor associated antigen(s) (TAA) extracted from human kidney carcinoma. Trypsinized human tumor cells were sonicated for 9 minutes and clarified at 100,000 x g for 1 hour; the supernate yielded 70% of detectable TAA as determined by means of quantitative absorption with specific antisera. The supernate used as source of soluble HSV-TAA was concentrated and the pellet was resuspended in 0.02 M tris, pH 7.2, and purified by means of filtration on Sephadex G-100 followed by chromatography on DEAE Sephadex A-50 and then affinity chromatography on concanavalin A (Con A) sepharose. The TAA bound to Con A sepharose was eluted by 0.5 M of alpha-CH3D-mannoside (alpha-MM) and behaved as a glycoprotein. The molecular weight determined on SDS-PAGE was about 70,000 daltons in relation to standard marker proteins. This antigen reacted in complement fixing tests with hyperimmune guinea pig sera as well as with certain human squamous cancer sera. As a control we used a human kidney carcinoma which showed no complement fixing activity in any of the procedural steps, and as control sera, guinea pig sera prepared by inoculation of uninfected guinea pig cells.

Antibodies specific for the carboxy- and amino-terminal regions of simian virus 40 large tumor antigen

Antibodies specific for the amino- and carboxy-terminal portions of simian virus 40 large tumor (T) antigen were obtained by immunization of rabbits with synthetic peptides corresponding to these regions. The amino-terminal synthetic peptide has the sequence Ac-Met-Asp-Lys-Val-Leu-Asn-Arg-(Tyr). The tyrosine residue was introduced in order to couple the peptide to bovine serum albumin with bis-diazotized benzidine. The carboxy-terminal peptide has the sequence Lys-Pro-Pro-Thr-Pro-Pro-Pro-Glu-Pro-Glu-Thr. It was coupled to bovine serum albumin with glutaraldehyde. The antisera against both peptides reacted with large T antigen. The specificity of the immune reaction was demonstrated by inhibition experiments using excess synthetic peptides. Furthermore, fragments of T antigen encoded by the nondefective adenovirus 2-simian virus 40 hybrid viruses Ad2+ND2 and Ad2+ND4, which contain the carboxy terminus and lack the amino terminus of large T antigen, were precipitated only with antiserum to the carboxy-terminal peptide. Small T antigen was not precipitated with either serum, suggesting that the amino terminus of small T antigen has a conformation different from that of large T antigen or that it is sterically hindered by a host protein. The procedures used here are of general importance for identification and characterization of gene product.

Relationship among Tau antigens isolated from various lines of simian virus 40-transformed cells

In addition to the virus-specified tumor antigens, simian virus 40-transformed cells contain at least one other protein which can be immunoprecipitated with serum from animals bearing simian virus 40-induced tumors. This protein, which is designated Tau antigen, has an apparent molecular weight of 56,000 as determined by electrophoresis on acrylamide gels. The relationship among Tau antigens isolated from different lines of simian virus 40-transformed cells was examined by comparing the methionine-labeled tryptic peptides of these proteins by two-dimensional fingerprinting on thin-layer cellulose plates. In this fashion, we initially determined that the Tau antigens isolated from three different lines of transformed mouse cells were very similar. Second, we found that Tau antigen isolated from a line of rat transformants was closely related, but not identical, to the mouse cell Tau antigens. Approximately 70% of their methionine peptides comigrated in two dimensions. Finally, we showed that Tau antigen isolated from a line of transformed human cells was only partially related to the mouse and rat proteins. About 40% of the methionine peptides of the human protein were also contained in the Tau antigens from the other two species. These results strongly indicate that the Tau antigens isolated from these various simian virus 40-transformed cell lines contain common amino acid sequences.

Mechanism of interferon action: simian virus 40-specific early polypeptides synthesized in untreated and interferon-treated monkey kidney cells

The effect of interferon treatment on proteins synthesized in simian virus 40 (SV40)-infected cells in the presence of cytosine arabinoside was investigated. The following results were obtained: (i) In addition to previously described large tumor (T) antigen (94 kilodaltons) and small tumor (t) antigen (19 kilodaltons), a 62-kilodalton polypeptide was immunoprecipitated by SV40 anti-T antiserum from extracts of infected CV-1 and BSC-1 monkey kidney cells and transformed SV3T3 mouse cells. The 94-, 62-, and 19-kilodalton polypeptides were not precipitated with normal serum from extracts of infected cells, and they were not present in extracts of uninfected cells. (ii) The de novo synthesis of the 94-, 62-, and 19-kilodalton tumor antigens was inhibited in CV-1 and BSC-1 cells treated with interferon before infection; total cellular protein synthesis was not significantly affected by interferon treatment. The relative interferon sensitivity of the three polypeptides in lytically infected monkey cells was comparable; by contrast, interferon did not affect their synthesis in transformed mouse cells. (iii) The 62-kilodalton polypeptide was detected in monkey cells infected with the following strains of SV40: tsA30 at both 33 degrees C and 41 degrees C; wt 708, the parent of tsA30; dI 884; and wt 830, the parent of dI 884. The amount of the 62-kilodalton species relative to T antigen was significantly greater in tsA30-infected cells as compared to cells infected with other SV40 strains. (iv) T, t, and 62-kilodalton polypeptides were readily labeled with [(35)S]methionine during a 10-min pulse; in a subsequent chase, the (35)S-labeled 94-kilodalton T antigen was apparently converted to 89- and 84-kilodalton polypeptides but not to either the 62-kilodalton polypeptide species or t antigen. (v) Partial peptide maps suggest that the 62-kilodalton polypeptide and T antigen are closely related. (vi) In addition to the above described 62-kilodalton polypeptide, a 54-kilodalton polypeptide was also detected. However, the 54-kilodalton species appears to be of cellular origin because it was immunoprecipitated with both normal and anti-T antiserum from uninfected and lytically infected cells and from virally transformed cells.

Simian virus 40 and polyoma virus stimulate overall cellular RNA and protein synthesis

In lytic infection with simian virus 40 and polyoma virus of monkey and mouse cells in tissue culture, synthesis of the viral tumor (T) antigens (T antigens) is rapidly followed by a mitogenic response of the host cell. The latter begins with virus-induced stimulation of overall cellular RNA and protein synthesis, leading to a substantial increase in cytoplasmic and nuclear RNA and protein. Stimulation begins within 1 hr after onset of T-antigen synthesis and also occurs if virus-induced DNA synthesis is blocked by metabolic inhibitors. The broad spectrum of biological and molecular effects induced by simian virus 40 and polyoma virus is, at least phenotypically, reminescent of the pleiotropic impact exerted on target cells by nonviral mitogens and by certain growth-promoting steroid and polypeptide hormones.

Specific association of simian virus 40 tumor antigen with simian virus 40 chromatin

Simian virus 40 tumor antigen (SV40 T antigen) was bound to both replicating and fully replicated SV40 chromatin extracted with a low-salt buffer from the nuclei of infected cells, and at least a part of the association was tight specific. T antigen cosedimented on sucrose gradients with SV40 chromatin, and T antigen-chromatin complexes could be precipitated from the nuclear extract specifically with anti-T serum. From 10 to 20% of viral DNA labeled to steady state with [3H]thymidine for 12 h late in infection or 40 to 50% of replicating viral DNA pulse-labeled for 5 min was associated with T antigen in such immunoprecipitates. After reaction with antibody, most of the T antigen-chromatin complex was stable to washing with 0.5 M NaCl, but only about 20% of the DNA label remained in the precipitate after washing with 0.5 M NaCl-0.4% Sarkosyl. This tightly bound class of T antigen was associated preferentially with a subfraction of pulse-labeled replicating DNA which comigrated with an SV40 form I marker. A tight binding site for T antigen was identified tentatively by removing the histones with dextran sulfate and heparin from immunoprecipitated chromatin labeled with [32P]phosphate to steady state and then digesting the DNA with restriction endonucleases HinfI and HpaII. The site was within the fragment spanning the origin of replication, 0.641 to 0.725 on the SV40 map.

Identification and partial characterization of new antigens from simian virus 40-transformed mouse cells

Two new species of antigens were detected in simian virus 40-transformed mouse cells, in addition to the large (94,000 daltons) and small (20,000 daltons) tumor antigens. These antigens were immunoprecipitated from cell extracts by using anti-T serum and not normal, nonimmune serum. One of these was a protein with a molecular weight of approximately 130,000 and was present in some but not all SV40-transformed mouse cells. The other, which we have named Tau antigen, has a molecular weight of 56,000 as estimated by electrophoresis through acrylamide gels and was found in all virus-transformed cells examined. The 13,000-daltons antigen contained about 15 methionine-tryptic peptides which were also present in the large SV40 tumor antigen as determined by ion-exchange chromatography. This strongly suggested that the protein was virus coded. The 56,000-dalton Tau antigen appeared to share only two methionine-tryptic peptides with the large species of SV40 tumor antigen, as determined by ion-exchange and paper chromatographies. Our results are compatible with a cellular origin for Tau antigen. However, our data do not exclude the possibility that this protein contains sequences specified by the virus DNA.

Effect of alkylation on the physical properties of simian virus 40 T-antigen species

We analyzed large and small species of T-antigen by immunoprecipitation and two-dimensional gel electrophoresis. The T-antigen species were subjected to electrophoresis either directly or after reduction and alkylation with N-ethylmaleimide. Treatment with N-ethylmaleimide improved the resolution of large-T by two-dimensional gel electrophoresis and was a requirement for the resolution of small-t antigen on two dimensional gels. Large-T did not form a discrete protein spot, but rather formed a streak from approximately pH 6.5 to 6.9 on isoelectric focusing gels. Small-t formed a sharp protein spot at approximately pH 7.2 when subjected to electrophoresis under non-equilibrium conditions which extended the pH gradient to include proteins with basic isoelectric points. Treatment with N-ethylmaleimide decreased the mobility of the T-antigen species during sodium dodecyl sulfate gel electrophoresis. We suggest that the apparent increase in molecular weight was due to the association of N-ethylmaleimide with cysteine-rich regions of these proteins. Viable deletion mutants of simian virus 40 which do not induce the synthesis of small-t but product small-t-related polypeptides were used to localize the cysteine-rich region of small-t to between 0.54 and 0.59 on the genetic map of simian virus 40.

Structural relationship between the 100,000- and 17,000- molecular-weight T antigens of simian virus 40 (SV40) as deduced by comparison with the SV40-specific proteins coded by the nondefective adenovirus type 2-SV40 hybrid viruses

The two-dimensional peptide maps of the methionine-containing tryptic peptides of the 100,000-molecular-weight (100K) and 17K T antigens of simian virus 40 (SV40) have been compared. The two proteins share nine methionine-containing tryptic peptides in common. The 17K T antigen has two peptides not found in the 100K T antigen, and the 100K T antigen has 14 unique peptides. The peptide maps of the 100 K and 17K T antigens were also compared with those of the SV40-specific proteins found in cells infected by the nondefective adenovirus type 2-SV40 hybrid viruses, which we have previously shown are encoded by defined sequences within the early region of SV40 (K. Mann, T. Hunter, G. Walter, and H.K. Linke, J. Virol. 24:151-169, 1977). This comparison shows that the 100K and 17K T antigens share common N-terminal sequences coded for between 0.65 and 0.59 map units on the SV40 genome. Furthermore, none of the sequences in the 17K T antigen arises from the region between 0.54 and 0.18 map units. We deduce that the sequences unique to the 17K T antigen originate between 0.59 and 0.54 map units. This type of structural relationship between the 100K and 17K T antigens fits well with the proposed model (L.V. Crawford, C.N. Cole, A. E. Smith, E. Paucha, P. Tegtmeyer, K. Rundell, and P. Berg, Proc. Natl. Acad. Sci. U.S.A. 75:117-121, 1978) for the expression of the early region of SV40.

Relationship between T-antigen and tumor-specific transplantation antigen in simian virus 40-transformed cells

The simian virus 40 (sv40) tumor antigen (T-antigen) and tumor-specific transplantation antigen (TSTA) have been partially purified and studied to clarify their relationship. The T-antigen and the TSTA were partially purified from nuclei of SV AL/N cells, and SV40-transformed mouse embryo fibroblast line, by precipitation with ammonium sulfate and chromatography on DEAE- and DNA-cellulose. The T-antigen was assayed by complement fixation, and the TSTA was assayed by its ability to immunize mice against SV40-containing ascites tumor cells. When T-antigen- and TSTA-containing preparations were sedimented through sucrose gradients, each antigen had a major peak of activity at a sedimentation coefficient of 6.7 and minor peaks in other regions. Antiserum against T-antigen (from tumor-bearing hamsters) immunoprecipitated the TSTA activity. A preparation of T-antigen from human SV80 cells, which exhibited only one protein band after sodium dodecylsulfate-polyacrylamide gel electrophoresis, had TSTA activity when as little as 0.6 microgram of protein per mouse was used for immunization. These experiments demonstrate that the T-antigen, the product of the SV40 early A gene is capable of inducing specific immunity against transplantation of SV40-transformed tumor cells in mice.

DNAs of simian virus 40 and polyoma direct the synthesis of viral tumor antigens and capsid proteins in Xenopus oocytes

Purified simian virus 40 and polyoma DNAs injected into nuclei of Xenopus oocytes were transcribed and subsequently translated into virus-specific tumor antigens and capsid proteins. Simian virus 40 large and small tumor antigens synthesized in the oocytes were indistinguishable, by gel electrophoresis and [35S]methionine-labeled tryptic peptide mapping, from the corresponding polypeptides synthesized in CV-1 African green monkey cells. The synthesis of large simian virus 40 tumor antigen implies the correct splicing of its mRNA, which is complementary to nonadjacent nucleotide sequences in the early region of the viral genome. Polyoma DNA directed synthesis of two polyoma tumor antigen polypeptides, 57,000 Mr and small tumor antigen, and of the main capsid protein.

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.

Measurements of the molecular size of the simian virus 40 large T antigen

A measure of the molecular weight of the large simian virus 40 T antigen was sought by SDS-polyacrylamide gel electrophoresis, random-coil chromatography, and sedimentation-velocity analysis in a density gradient. Large T antigen obtained from a simian virus 40-transformed human cell line either by immunoprecipitation or by standard preparatory methods migrated like a 94,000-molecular-weight (approximately 94K) polypeptide in SDS-gels but was found to have an approximate was observed with T antigen obtained from lytically infected monkey cells. In view of the strong theoretical basis for the guanidine method and the agreement with the sedimentation data, these findings suggest that the molecular weight of this protein is approximately 75 to 80K as opposed to 94 to 100K and, therefore, that considerably less than the entire early region of simian virus 40 is required to encode it. This size estimate is in keeping with earlier results which revealed a normal-size T antigen in cells infected with viable deletion mutants lacking as much as 10% of the early region.

Role of the simian virus 40 gene A product in regulation of DNA synthesis in transformed cells

Cells transformed by tsA mutants of simian virus 40 (SV40) are temperature sensitive for the maintenance of the transformed phenotype. The kinetics of induction of DNA synthesis were determined for hamster cell transformants shifted to the permissive temperature after a 48-h serum arrest at the nonpermissive temperature. DNAsynthesis was initiated in the tsA transformants by 8 h after shiftdown was maximal by 12 h. The presence or absence of fetal bovine serum at the time of temperature shift had no effect on the kinetics of initiation of DNA synthesis. Analysis of TTP in tsA transformants revealed similar levels of incorporation of [3H]thymidine into TTP at both permissive and nonpermissive temperatures. Autoradiography revealed that by 12 h after a shift to the permissive temperature, approximately 50% of the cells exhibited labeled nuclei after a 60-min pulse with [3H]thymidine, indicating that a majority of the cells were actively synthesizing DNA. By 8 to 12 h after a shiftup of confluent tsA transformants to the nonpermissive temperature, the number of labeled nuclei was reduced to approximately 16%, regardless of serum concentration. These data indicate that the SV40 gene A product, either directly or indirectly, regulates cellular DNA synthesis in transformed cells.

The genome of simian virus 40

The nucleotide sequence of SV40 DNA was determined, and the sequence was correlated with known genes of the virus and with the structure of viral messenger RNA's. There is a limited overlap of the coding regions for structural proteins and a complex pattern of leader sequences at the 5' end of late messenger RNA. The sequence of the early region is consistent with recent proposals that the large early polypeptide of SV40 is encoded in noncontinguous segments of DNA.

Simian virus 40 (SV40)-specific proteins associated with the nuclear matrix isolated from adenovirus type 2-SV40 hybrid virus-infected HeLa cells carry SV40 U-antigen determinants

The distribution of simian virus 40 (SV40)-specific proteins in nuclear subfractions of pulse-chase-labeled HeLa cells infected with nondefective adenovirus type 2 (Ad2)-SV40 hybrid viruses was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The SV40-specific proteins of Ad2+ND1, Ad2+ND2, and Ad2+ND5 specifically associate with the nuclear matrix and are virtually absent from the high-salt nuclear extract. In Ad2+ND4-infected HeLa cells, the SV40-specific proteins with molecular weights of 64,000 (64K) and lower also specifically associate with the nuclear matrix. The SV40-specific 72K, 74K, and 95K proteins were found both in the nuclear matrix and in the high-salt nuclear extract. Analyses of the nuclear matrices isolated from hybrid virus-infected cells by immunofluorescence microscopy showed that SV40 U-antigen-positive sera from SV40 tumor-bearing hamsters react with SV40-specific proteins integrated into nuclear matrices of HeLa cells infected by Ad2+ND1, Ad2+ND2, and Ad2+ND4, but not with nuclear matrices of HeLa cells infected by Ad2+ND5. This suggests that SV40-specific proteins of Ad2+ND1, Ad2+ND2, and Ad2+ND4 integrated into the nuclear matrix carry SV40 U-antigen determinants. The apparent discrepancy in the subcellular localization of SV40-specific proteins in hybrid virus-infected cells when analyzed by biochemical cell fractionation procedures and when analyzed by immunofluorescence staining is discussed.

T antigen of BK papovavirus in infected and transformed cells

BK virus T antigen from BKV-transformed rat and hamster cells and from productively infected monkey cells has been examined by immunoprecipitation followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Forms of the antigen that migrate as proteins of 86,000 and 92,000 daltons have been identified. Both forms can be labeled by 32P.

Common methionine-tryptic peptides near the amino-terminal end of primate papovavirus tumor antigens

The tumor antigens directed by human papovaviruses BK and JC and the monkey papovavirus simian virus 40 have two methionine-containing tryptic peptides in common. These peptides are constituents of the small forms of papovavirus tumor antigen (17,000 daltons) which are present in lytically infected and transformed cells and which are believed to share some amino acid sequences with the amino-terminal portion of the larger tumor antigen species (97,000 daltons). In addition to the two peptides, which are present in all three papovavirus tumor antigens, the larger forms of the tumor antigens specified by simian virus 40 and BK virus share four other methionine-containing tryptic peptides, two of which are also present in the smaller (17,000 daltons) species of antigen. The occurrence of common peptides at the amino-terminal portion of tumor antigens of primate papovaviruses suggests that these conserved regions may play a fundamental role in the function of these proteins and in the propagation of these viruses in nature. The tryptic peptides of the small forms of papovavirus tumor antigen were examined and compared to those present in the large species. Out of a total of nine and ten methionine-containing peptides in the 17,000-dalton tumor antigens of simian virus 40 and BK virus, seven and nine peptides, respectively, are constituents of the corresponding larger (97,000 daltons) forms of the antigen.

Tumor antigen(s) in cell productively infected by wild-type polyoma virus and mutant NG-18

When isolated by means of an anti-polyoma tumor (T) antiserum, the major product from mouse cells productively infected by wild-type polyoma virus is a polypeptide of 100,000 apparent molecular weight as judged by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. In cells infected by NG-18, an hr-t mutant carrying a deletion of about 150 base pairs in the early region of the viral DNA, a T antigen species appears that comigrates with that of the wild-type virus. Comparisons of peptides after partial proteolysis reveal no differences between mutant and wild-type products. Both wild-type and mutant 100,000 products can be labeled in vivo with [(32)P]orthophosphate. An independent and more reliable estimate of the molecular weight of this protein using guanidine/Sepharose chromatography yields a value of 81,000 for both mutant and wild-type species. The apparent identity of wild-type and mutant products indicates that the deletion in NG-18 lies outside of the region encoding this major T antigen species. Immunoprecipitates from wild-type infected cells shows four bands in addition to the "100,000" band; these have apparent molecular weights of 63,000, 56,000, 36,000, and 22,000 by sodium dodecyl sulfate/polyacrylamide gel electrophoresis; the 56,000 and 36,000 species are phosphorylated. All four of these lower molecular weight bands are absent or drastically reduced in the immunoprecipitates from NG-18-infected cells.

In vivo and in vitro TSTA-inducing activity of temperature-sensitive (ts) mutants of SV40

In vivo TSTA induction in Syrian hamsters was studied with the use of SV40 ts mutants (A, B, C, BC and D). The ts A30, TS A239 and possibly also the ts BC210 mutants were defective in resistance-inducing activity in hamsters in contrast to wild type SV40 and other ts mutnats. At the permissive temperature ts A30 and ts A239 did not induce TSTA in hamster cells during abortive infection in vitro, while they did so in green monkey cells at both permissive and non-permissive temperatures. In hamster cells transformed by ts A30, ts A239 and ts A209 mutants none at all or very little TSTA was detected by in vivo transplantation immunological tests. Thus, expression of TSTA induced by these three SV40 ts A mutants was found to be dependent from the species of infected cells and was being a temperature independent viral function.

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.

Relationship between the methionine tryptic peptides of simian virus 40 and BK virus tumor antigens

The monomer form of BK virus (BKV) tumor antigen (T Ag) was immunoprecipitated from extracts of BKV-transformed cells and had a molecular weight of approximately 113,000. This compared with 97,000 for the molecular weight of either BKV or simian virus 40 (SV40) T Ag from lytically infected cells. The SV40 and BKV T Ag's from productively infected cells were compared by examining their methionine-labeled tryptic peptides. Out of a total of 20 SV40-and 21 BKV-specific peptides, there were seven pairs of similar peptides on the basis of ion-exchange chromatography, These coeluting peptides contained approximately 25 to 30% of the total methionine radioactivity. Similar results were obtained when the tryptic peptides of SV40 T Ag from lytically infected cells were compared with those of BKV T Ag from virally transformed cells.

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.

Purification of simian virus 40 tumor antigen from a line of simian virus 40-transformed human cells

Simian virus 40 tumor antigen can be isolated in a highly purified state from the nuclei ofSV80 cells, a continuous line of simian virus 40-transformed human fibroblasts. A five-step purification method was used. Its apparent molecular weight (in sodium dodecyl sulfate/polyacrylamide gels) is approximately 90,000-94,000. It contains a detectable amino-terminal residue.

Interaction of polyoma and mouse DNAs. IV. Time course and extent of integration of polyoma DNA into mouse DNA during lytic infection

The time course of covalent binding of polyoma viral DNA to mouse DNA was followed in mouse embryo cells that had been grown prior to infection in the presence of 5-bromodeoxyuridine. Density-labeled (HL) mouse DNA was separated from free polyoma DNA by CsCl isopycnic centrifugation. Polyoma DNA sequences present in HL mouse DNA were detected by hybridization with radioactive cRNA synthesized in vitro. In reconstruction experiments, the limit of detection was found to be, on the average, about 0.5 genome equivalent (g.e.) of polyoma DNA per cell. To find conditions for the isolation of HL mouse DNA and for its complete separation from free polyoma DNA, cultures infected at 4 degrees C were used. HL mouse DNA extracted with sodium dodecyl sulfate and high salt concentrations (5 to 6 M CsCl) and then purified by three consecutive CsCl density gradient centrifugations was free from detectable amounts of polyoma DNA, whereas HL mouse DNA extracted with chloroform and phenol and purified in the same way always contained contaminating, noncovalently bound polyoma DNA. In lytically infected bromodeoxyuridine-prelabeled mouse embryo cultures, polyoma DNA bound to HL mouse DNA that had been extracted by the sodium dodecyl sulfate-CsCl procedure was first detected in small amounts (1 to 2 g.e. per cell) at 10 h after infection. In cultures incubated with medium containing thymidine (5 mug/ml), 4 to 6 g.e. of polyoma DNA per cell was detected at 14 and 18 h after infection. In these samples, practically all viral DNA was bound to high-molecular-weight HL mouse DNA. In cultures incubated with normal medium (no additions) and extracted between 17 and 20 h after infection, 20 to 350 g.e. of polyoma DNA per cell banded with HL mouse DNA. However, when DNA of one of these samples was subfractionated by sodium dodecyl sulfate-salt precipitation prior to isolation of HL mouse DNA, about 80% of the viral DNA banding at increased density was present in the low-molecular-weight DNA fraction. This observation suggests that in normal medium some progeny viral DNA of increased density was synthesized. Covalent binding of polyoma DNA to density-labeled mouse DNA was demonstrated by alkaline CsCl density gradient centrifugation: nearly equal amounts of polyoma DNA were found in the H and L strands, respectively, as is expected for linear integration of viral DNA. The results lead to the conclusions that (i) early polyoma mRNA is transcribed from free parental viral DNA; (ii) covalent linear integration is first detectable at the time when tumor (T)-antigen is synthesized; and (iii) only few copies (<10 g.e./cell) become integrated between 10 and 18 h after infection, i.e., during the period when cellular and viral DNA replication starts in individual 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.

Simian virus 40 gene A regulates the association between a highly phosphorylated protein and chromatin and ribosomes in simian virus 40-transformed cells

The species of proteins associated with chromatin and ribosomes of simian virus 40 (SV40)-transformed and untransformed monkey, mouse, and rat cells have been compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis after phosphorylation of these proteins either in vivo or in vitro. In vitro phosphorylation was carried out by protein kinase associated with these organelles and [gamma-(32) P]ATP as the phosphoryl donor. The reaction products contained both phosphoserine and phosphothreonine in approximately equal amounts. The electrophoretic analysis of the phosphorylated proteins revealed that the highly phosphorylated protein with a molecular weight of approximately 90,000 (90K protein) was associated with chromatin and ribosomes from transformed cells but not from untransformed cells. The 90K protein could be extracted from chromatin and ribosomes with 0.5 to 1.0 M NaCl or KCl. The 90K protein was still associated with the runoff ribosomes prepared by the puromycin reaction of the post-mitochondrial supernatant in the protein-synthesizing system. In vitro phosphorylation of chromatin and ribosomes from SV40 tsA-transformed mouse and rat cells indicated that the amounts of 90K protein associated with these organelles decreased greatly when the cells were cultivated at the restrictive temperature. A similar temperature-dependent decrease in the amount of (32)P-labeled 90K protein was observed in nonhistone chromosomal and ribosome-associated protein fractions prepared from SV40 tsA-transformed cells labeled with [(3)H]leucine and [(32)P]orthophosphate in vivo. In vitro phosphorylated 90K protein in nonhistone chromosomal and ribosome-associated proteins extracted with high salt was not immunoprecipitated with anti-SV40 T sera.

Polyoma-induced stimulation of cellular RNA synthesis is paralleled by changed expression of the viral genome

We studied synthesis of viral and cellular RNA in the presence and absence of 5-fluorodeoxyuridine (FdU, an inhibitor of DNA synthesis) during lytic infection with polyoma virus in confluent, primary mouse kidney cell cultures. In the presence of FdU, synthesis of early 19S polyoma mRNA and of polyoma tumor (T)-antigen, i.e. expression of the early viral gene, is rapidly followed by a mitogenic reaction of the host cell; it leads to an increase of 30 +/- 5% in cellular, mainly 28S and 18S rRNA, followed by activation of the cellular DNA-synthesizing apparatus. Polyoma-induced cellular RNA synthesis is paralleled by increased production of early 19S mRNA and begin of expression of the late viral genes, leading to synthesis of small amounts of late 19S and 16S mRNAs. Changed expression of the viral genome occurs in the absence of detectable synthesis of polyoma DNA I. Infection in the absence of FdU induces the same sequence of events; it is followed, however, by duplication of the mouse cell chromatin (S-phase) and production of progeny virus.

Identification of a purified complement-fixing antigen as the Epstein-Barr-virus determined nuclear antigen (EBNA) by its binding to metaphase chromosomes

A soluble complement-fixing antigen carried by Epstein-Barr virus (EBV)-transformed human cells has been previously extracted from cell nuclei and purified by DNA-cellulose chromatography [Luka, J., Siegert, W. & Klein, G. (1977) J. Virol., in press]. On addition of this antigen to methanol/acetic acid-fixed metaphase chrmosomes, followed by exposure to human sera containing antibodies against the EBV-determined nuclear antigen (EBNA), brilliant positive staining was obtained by anti-complement immunofluorescence. There was no staining after exposure to EBV-negative sera. Moreover, a nuclear protein fraction, prepared from an EBV-negative cell line in an analogous fashion, failed to induce the staining reaction. These data identify the soluble purified antigen as the EBV-determined nuclear antigen. The purified antigen has a molecular weight of 174,000 +/- 15,000, as determined by sucrose gradient centrifugation and gel filtration experiments. In neutral buffers containing 0.5-1.0 M NaCl, the antigen dissociates into a form of approximately one-half the original molecular weight with retained complement-fixing activity. This "monomer" has a molecular weight of 98,000 +/- 8,000.

Characterization of polyoma virus T antigen

High-titer antiserum raised in rats against the tumor (T) antigen of polyoma virus was used to purify the T antigen by the Staphylococcus protein A antibody adsorbent technique. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis allowed the identification of a protein with an apparent molecular weight of 100,000-108,000 as a major component induced in lytically infected mouse cells. In cells infected by ts A mutants this component was temperature sensitive. Several minor components were also observed. In pulse and chase experiments there was a slight decrease in electrophoretic mobility of T antigen during the chase period at the permissive temperature, suggesting that the T antigen is a modified protein. In two lines of transformed cells, the amount of T antigen seemed to be considerably less than in lytically infected cells, but the size of the antigen appeared to be equal.

Modification of simian virus 40 protein A

The A protein of simian virus 40 is phosphorylated in both productive and transforming infection. The phosphorylated amino acid has been identified as serine and has been localized in a single tryptic peptide of the protein. Because the A protein synthesized in infection by A mutants is phosphorylated to the same extent and in the same peptide as in infection by wild-type virus, the functional defect of the A mutants is apparently unrelated to phosphorylation. At least three distinct forms of the A protein with apparent molecular weights of 85,000, 88,000, and 100,000 can be identified in extracts of cells infected by wild-type virus. After exposure of cells to Nonidet P-40, the 85,000- and 88,000-dalton proteins were found in varying amounts in extracts of permissive cells but not in extracts of transformed cells. This finding raised the question of the possible functional importance of the smaller proteins in productive infection. However, the virtual absence of the 85,000- and 88,000-dalton proteins in some extracts of the fully permissive CV-1 cell line indicates that a conversion of the larger to the smaller forms of the A protein is not required in significant quantity for productive infection. Furthermore, a study of extraction conditions shows that the smaller proteins are easily generated during extraction and provides an explanation for the appearance of these proteins in some cells after extraction under unfavorable conditions.

Cell-free translation of simian virus 40 early messenger RNA coding for viral T-antigen

Simian virus 40 (SV40) mRNA was isolated by hybridization of cytoplasmic RNA, from SV40-infected BS-C-1 monkey cells early in lytic infection, to SV40 DNA immobilized on Sepharose. The early viral mRNA, when added to a wheat-germ translation system, directed the synthesis of a unique class of products including a 90,000 molecular weight (Mr) polypeptide. It was found that this 90,000 Mr product as well as a prominent 17,000 Mr polypeptide could be specifically immunoprecipitated with hamster antiserum to SV40 T-antigen, but not with hamster control serum. Similar immunoprecipitation of extracts of SV40-infected cells with hamster anti-T serum yielded 90,000 Mr and 17,000 Mr polypeptides; these polypeptides were not found in immunoprecipitates of uninfected cell extracts. SV40 cRNA, prepared by asymmetric transcription of plaque-purified SV40 DNA, directed the cell-free synthesis of several products, including a 70,000 Mr polypeptide that could be specifically immunoprecipitated with anti-T serum. However, no T-antigen-related polypeptide was found in infected cells that corresponded in size to the major immunoprecipitated cRNA product.