Immunological identification of two adenovirus 2-induced early proteins possibly involved in cell transformation

Specific proteolytic fragmentation of p60v-src in transformed cell lysates

Work involving the transforming protein, p60v-src, of Rous sarcoma virus has resulted in the extensive characterization of its protein structure and associated phosphotransferase activity. However, in many investigations proteolytic fragments (principally p52v-src) of the src protein are actually studied. Here, we emphasize potential problems in the interpretation of experimental results in which the proteolytic fragmentation of p60v-src may be involved and offer several means for the complete prevention of this p60v-src degradation.

Different structural systems of the nucleus are targets for SV40 large T antigen

To define the interaction of SV40 large T with different structural systems in the nuclei of SV40-transformed cells (BALB/c mKSA), we have employed an in situ cell fractionation procedure leading to the preparation of the nuclear matrix, and giving rise to defined nuclear extracts comprising soluble nuclear proteins (nucleoplasm) and the solubilized chromatin. Large T could be detected in the nucleoplasmic fraction and in the chromatin fraction, as well as in tight association with the nuclear matrix. From the nuclear matrix, large T could be solubilized by treatment with a zwitterionic detergent. Different solubility properties, differences in the amount of the cellular phosphoprotein p53 coprecipitating with large T, and different stabilities in its association with the nuclear structural systems indicate that distinct subclasses of large T were isolated from their in vivo location in SV40-transformed cells.

Acylation: a new post-translational modification specific for plasma membrane-associated simian virus 40 large T-antigen

SV40 transformed mouse cells (mKSA) were labeled in parallel with either [35S]methionine or [3H]palmitate and subfractionated. Nuclear extracts and solubilized plasma membranes were analyzed for the presence of either 35S- or 3H-labeled SV40 large tumor antigen by immunoprecipitation and SDS polyacrylamide gel electrophoresis. The majority of the [35S]methionine labeled large T was recovered from the nuclear fraction, only minor amounts were detected in plasma membranes. In contrast, large T labeled specifically with [3H]palmitate was found only in the plasma membrane fraction. Our results demonstrate a specific acylation of large T associated with plasma membranes, suggesting that the membrane location of this predominantly nuclear protein is specific.

Immunoprecipitation of proteins from cell-free translations

A typical procedure for immunoprecipitating a protein (abundance ca 0.5%) synthesized in the wheat germ cell-free system is summarized below. 1. Two microliters of 25% SDS are added to 48 microliters of translation reaction mixture, and the sample is heated to 100 degrees for 4 min. 2. Four volumes (i.e., 200 microliters) of dilution buffer at 4 degrees are added to the above sample. Dilution buffer is 1.25% Triton X-100, 190 mM NaCl, 60 mM Tris-HCl, pH 7.4, 6 mM EDTA, 10 units of Trasylol per milliliter. 3. Five microliters of appropriate antisera are added, and the sample is incubated for at least 12 hr at 4 degrees. 4. The sample is spun for 2 min in a microcentrifuge, and the supernatant is transferred to a fresh tube. 5. Thirty microliters of a 1 : 1 suspension of protein A-Sepharose CL-4B (15 microliters of packed beads) are added, and the sample is incubated with end-over-end mixing at room temperature for 2 hr. 6. The Sepharose beads are pelleted by a 10-sec centrifugation in the microcentrifuge, and the supernatant is aspirated. 7. The beads are washed four times in 1 ml, per wash, of 0.1% Triton X-100, 0.02% SDS, 150 mM NaCl, 50 mM Tris-HCl, pH 7.5, 5 mM EDTA, 10 units of Trasylol per milliliter at room temperature with vortexing at each wash. 8. The beads are given a final wash with the above solution not containing detergent, and the supernatant is aspirated as completely as possible with a drawn-out Pasteur pipette. 9. Forty microliters of SDS-gel electrophoresis sample buffer containing 50 mM DTT are added to the beads, and the sample is heated for 4 min in a boiling water bath. 10. Free--SH groups are blocked by adding 10 microliters of 1.0 M iodoacetamide in sample buffer and incubating for 45 min at 37 degrees. 11. The beads are centrifuged out, and the supernatant is applied to an SDS-polyacrylamide slab gel.

Hyperproduction of adenovirus type 12 E1B gene product in monkey cells, using a simian virus 40 vector

Simian virus 40 recombinant DNAs carrying the adenovirus type 12 E1B gene were constructed, propagated, and packaged in monkey cells. Monkey cells infected with the resulting virus stocks hyperproduced the E1B gene products in more than 80% of the cells as revealed by immunofluorescence. The products were distributed in both the nuclei and the cytoplasm, and a condensed form of fleck structure was observed in the cytoplasm. Polyacrylamide gel electrophoresis of the cell extracts and their immunoprecipitates detected the E1B-coded 19,000-molecular-weight protein but not the 50,000-molecular-weight protein. The 19,000-molecular-weight protein and the simian virus 40 VP1 protein were synthesized in nearly equal amounts.

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.

Localization of viral structural proteins in the cytoplasm and nucleus of Rous-associated virus-2-infected chicken embryo fibroblasts

The cellular location of viral structural proteins was carried out by immunohistochemistry and by cell fractionation. Antibody against the structural protein p27 was used in immunohistochemical reactions to demonstrate the presence of viral proteins in the cytoplasm and nucleus of Rous-associated virus 2-infected chicken cells. Localization in the nucleus was found over heterochromatic regions; in the cytoplasm it was found in discrete particulate structures. These observations were extended in cell fractionation studies in which cytoplasmic and nuclear fractions were immunoprecipitated with antibody against the viral structural proteins.

Biosynthesis of virus-specific proteins in cells infected with infectious bursal disease virus and their significance as structural elements for infectious virus and incomplete particles

It has previously been shown that infectious bursal disease virus is a naked icosahedral particle with a diameter of about 60 nm and a genome consisting of two segments of double-stranded RNA (Müller et al., J. Virol. 31:584-589, 1979). One of the two major structural polypeptides (molecular weight, 40,000) of this virus could not be found in lysates of infected cells; it is derived from a precursor polypeptide demonstrable inside the cells in relatively large quantities and seems to be processed during virus assembly or later. The precursor molecule is regularly present in the infectious virus particle (buoyant density, 1.33 g/ml) in minor proportions, but it represents an outstanding structural element of incomplete noninfectious particles ("top components"; buoyant density, 1.29 g/ml) which contain viral RNA. This type of incomplete particles is mainly produced by chicken embryo fibroblasts in contrast to lymphoid cells from the bursa of Fabricius. Precursor-product relationships also seem to exist in the biosynthesis of the other viral polypeptides. In contrast to some other viruses with a segmented double-stranded RNA genome, none of the structural proteins of infectious bursal disease virus is appreciably glycosylated.

Purification of a native membrane-associated adenovirus tumor antigen

A 15,000-dalton protein was purified from HeLa cells infected with adenovirus type 2. Proteins solubilized from a membrane fraction of lytically infected cells was used as the starting material for purification. Subsequent purification steps involved lentil-lectin, phosphocellulose, hydroxyapatite, DEAE-cellulose, and aminohexyl-Sepharose chromatographies. A monospecific antiserum, raised against the purified protein, immunoprecipitated a 15,000-dalton protein encoded in early-region E1B (E1B/15K protein) of the adenovirus type 2 DNA. Tryptic finger print analysis revealed that the purified protein was identical to the E1B/15K protein encoded in the transforming part of the viral genome. The antiserum immunoprecipitated the E1B/15K protein from a variety of viral transformed cell lines isolated from humans, rats, or hamsters. The E1B/15K protein was associated with the membrane fraction of both lytically and virus-transformed cell lines and could only be released by detergent treatment. Furthermore, a 11,000- to 12,000-dalton protein that could be precipitated with the anti-E1B/15K serum was recovered from membranes treated with trypsin or proteinase K, suggesting that a major part of the E1B/15K protein is protected in membrane vesicles. Translation of early viral mRNA in a cell-free system, supplemented with rough microsomes, showed that this protein was associated with the membrane fraction also in vitro.

Characterization of measles virus-specific antibodies in sera from patients with chronic active hepatitis

Measles virus-specific antibodies in sera from patients with HBsAg-negative chronic active hepatitis and raised antibody titres against measles virus, have been examined by crossed immunoelectrophoresis. The immunoprecipitates were further analysed by SDS-polyacrylamide gel electrophoresis. Five measles virus-specific precipitation lines were demonstrated using measles virus-infected cells solubilized with Triton X-100. The three major precipitation lines were analysed by SDS-PAGE and contained the virus polypeptides: nucleoprotein, NP (MW approximately 60 000); haemoagglutinin, H (MW approximately 80 000) and fusion protein F1 (MW approximately 40 000). Considerably higher amounts of antibodies against these three virus polypeptides were demonstrated in the patient sera than in sera from healthy controls. By SDS-PAGE analysis of radiolabelled immune complexes adsorbed to Sepharose-protein A, antibodies against five measles virus polypeptides: NP, H, F1, P protein (MW approximately 70 000) and matrix protein, M (MW approximately 37 000) were demonstrated in the patient sera.

Identification and purification of a protein encoded by the human adenovirus type 2 transforming region

The human adenovirus type 2 (Ad2) transforming genes are located in early regions E1a (map position 1.3 to 4.5) and E1b (map position 4.6 to 11.2). We have identified and purified to near homogeneity a major 20,000-molecular-weight (20K) protein and have shown that it is coded by E1b. Using an Ad2-transformed cell antiserum which contained antibody to E1b-coded proteins, we immunoprecipitated 53K and 19K proteins from the nucleoplasm and 53K, 19K, and 20K proteins from the cytoplasmic S-100 fraction of Ad2 productively infected and Ad2-transformed cells. The 19K protein was present in both the nucleoplasm and the cytoplasm, whereas the 20K protein was found only in the cytoplasm. The 53K and 19K proteins are known Ad2 E1b-coded proteins. The 20K protein was purified to near homogeneity in 20 to 50% yields by sequential DEAE-Sephacel chromatography and reverse-phase high-performance liquid chromatography. Purified 20K protein shares most of its methionine-labeled tryptic peptides with E1b-53K, as shown by reverse-phase high-performance liquid chromatography, and therefore is closely related to the 53K protein. The 19K protein does not appear to share tryptic peptides with either 20K or 53K protein. To provide more direct evidence that 20K protein is virus-coded, we translated E1b-specific mRNA in vitro. Both immunoprecipitation analysis and high-performance liquid chromatography purification of the translated product identified a 20K protein that has the same tryptic peptides as the 20K protein isolated from infected and from transformed cells. These findings suggest that the Ad2 20K protein is a primary translation product of an Ad2 E1b mRNA.

Adenovirus E1b-58kd tumor antigen and SV40 large tumor antigen are physically associated with the same 54 kd cellular protein in transformed cells

The adenovirus E1b-58kd tumor antigen has been detected in a physical association with a 54 kilodalton cellular protein in adenovirus-transformed mouse cells. Antibody specific for the E1b-58kd protein coimmunoprecipitates a 54 kd protein from transformed, but not from productively infected, cells. Monoclonal antibody specific for the cellular 54 kd protein coimmunoprecipitates the adenovirus E1b-58kd protein from transformed cell extracts. The same or closely related cellular 54 kd protein, associated with the adenovirus E1b-58kd protein, was present in the SV40 large T antigen-54 kd complex previously detected in SV40-transformed mouse cells. The identity of the 54 kd protein is based on the immunological specificities of the anti-54 kd monoclonal antibodies and partial peptide maps of the 54 kd protein associated with the adenovirus and SV40 tumor antigens. The adenovirus E1b-58kd-54 kd complex, like the SV40 large T antigen-54 kd complex, is heterogeneous in size or mass. While all of the cellular 54 kd protein in the adenovirus-transformed cell extract is found in a complex with the E1b-58kd protein, some of the viral 58 kd antigen is detected in a form not associated with the 54 kd protein. The fact that the adenovirus and Sv40 tumor antigens, both required for transformation, can be found in physical association with the same cellular protein in a transformed cell is a good indication that these two diverse viral proteins share some common mechanisms or functions.

Unique glycoprotein-proteoglycan complex defined by monoclonal antibody on human melanoma cells

A monoclonal antibody, 9.2.27, with a high specificity for human melanoma cell surfaces has been utilized for biosynthetic studies in M21 human melanoma cells to define a unique antigenic complex consisting of a 250-kilodalton N-linked glycoprotein and a high molecular weight proteoglycan component larger than 400 kilodaltons. The 250-kilodalton glycoprotein has endoglycosidase H-sensitive precursors and shows a lower apparent molecular weight after treatment with neuraminidase. The biosynthesis of the proteoglycan component is inhibited by exposure of M21 cells to the monovalent ionophore monensin, this component can be labeled biosynthetically with 35SO4, is sensitive to beta-elimination in dilute base, and is degraded by both chondroitinase AC and ABC lyases, suggesting that it is a chondroitin sulfate proteoglycan. These data demonstrate that the antigenic determinant recognized by monoclonal antibody 9.2.27 is located on a glycoprotein-proteoglycan complex which may have unique implications for the interaction of glycoconjugates at the human melanoma tumor cell surface.

Immunochemical and biosynthetic analysis of monoclonal antibody-defined melanoma-associated antigen

Immunoprecipitation studies with application of monoclonal antibody F11 originally made to a partially purified spent medium antigen of melanoma cells, made it possible to delineate the molecular profiles of both the cell associated and spent medium antigens recognized on melanoma cells intrinsically labeled with glycoprotein precursors. F11 distinguishes a glycoprotein of Mr 100,000 (100 K) in the spent media of melanoma cells while a parallel analysis of detergent lysates of cells reveals a pattern of three glycoproteins of Mr 75, 77, and 100 K. Pulse-chase analysis of the biosynthesis of these antigens indicated that F11 first recognizes the 75 and 77 K antigens in the absence of a 100K component suggesting strongly that these molecules contain an antigenic site recognized by F11. The 100 K antigen appears later in the pulse-chase analysis with kinetics that suggest some of the 75 and 77 K antigens are biosynthetic precursors of the 100 K antigen. This molecule is ultimately secreted into the extracellular media and appears to be a sialoglycoprotein judging from its sensitivity to neuraminidase. A cross-reactive species with an approximate Mr 90 K is also recognized by F11 in indirect immunoprecipitation analysis of spent media from a neuroblastoma cell line indicating that a common antigenic site exists on this secreted but structurally different neuroblastoma antigen. Thus, a combination of immunochemical and biosynthetic analyses of cell-associated and secreted antigens recognized by monoclonal antibody F11 demonstrate such molecules can differ structurally when isolated from the same or different tumor cells. These findings indicate the necessity to establish molecular profiles of melanoma-associated glycoprotein antigens recognized by monoclonal antibodies to characterize and define their potential biological functions within tumor cells.

Immunochemical properties of antigens present on immature erythrocytes from mouse and rat

Rabbit antisera directed against erythrocytes from anemic mice or from newborn rats, once absorbed on homologous normal adult erythrocytes, recognize antigens present respectively on immature erythrocytes from anemic adult mice or rats (Im M and Im R antigens). Using iodinated immature erythrocytes from both species, homologous sera precipitated two populations of antigens showing 230,000 D and 95,000 D molecular weights. Im M antigens (230,000 and 95,000 D) were partially precipitated using anti-Im R serum. After total absorption of the sample by anti-Im R serum, both 230,000 and 95,000 D antigens were still immunoprecipitated using anti-Im M serum. Similar results were obtained using Im R antigens and anti-Im M serum then anti-Im R serum. This demonstrates that some Im specificities are common to rat and mouse while others, showing identical molecular weights, are species-specific.

Control of adenovirus early gene expression: accumulation of viral mRNA after infection of transformed cells

We studied the accumulation of viral mRNA in the presence of inhibitors of protein synthesis in an adenovirus type 5-transformed cell line (line 293 cells). An analysis of the endogenous viral mRNA's and proteins revealed that only early regions 1A and 1B were expressed in uninfected 293 cells. However, viral mRNA's from early regions 2, 3, and 4, as well as mRNA's from early regions 1A and 1B, accumulated in 293 cells after infection with adenovirus type 2. Cells treated with anisomycin before infection showed a drastic enhancement of mRNA from early region 4 compared with drug-free controls, This increase in viral mRNA was detected by using filter hybridization, S1 endonuclease mapping, and in vitro translation. The rate of transcription of early region 4 nuclear RNA also increased significantly in the presence of anisomycin. In contrast to the results with early region 4, the levels of cytoplasmic mRNA's from early regions 2 and 3 did not increase in cells treated with inhibitors. These results suggested that multiple virus encoded controls operate on the early regions of the adenovirus genome.

Purification of measles virus H polypeptide and of F polypeptide

Measles virus was disrupted by Tween 80 and ether and subjected to isoelectric focusing in granular gel. The two surface envelope polypeptides, the one showing haemagglutinating activity (H) and the one making up the structural basis of the haemolytic and fusion activity (F) banded together at pH 5.2. The two envelope polypeptides were also isolated together after adsorption to a Lentil-lectin column. Separation of the two polypeptides was performed by gel filtration on Sephadex G-150 in the presence of 8 M urea. After separation both the H and F polypeptides fixed to the lectin column. It was demonstrated that the column, after having fixed the two polypeptides, absorbed anti-H and anti-F antibodies from a rabbit anti-measles virus immune serum. Thus the antigenic reactivity of the isolated surface polypeptides remained intact.

Adenovirus early gene products may control viral mRNA accumulation and translation in vivo

The mechanisms controlling early adenovirus gene expression in vivo have been studied using inhibitors of protein synthesis. When inhibitors were added shortly before or at the onset of infection, viral mRNA from all early regions was transcribed, spliced and accumulated over a 7 hr period. After longer pretreatment, accumulation of several early mRNAs were suppressed. Addition of inhibitors 1 hr after infection enhanced the accumulation of viral mRNA in the cytoplasm. Translation of early mRNA selected on adenovirus DNA in a cell-free system reflected the amount of viral mRNA present. A viral coded product may therefore control accumulation of viral mRNA. A different pattern emerged when inhibitors of protein synthesis were removed at 5 hr postinfection and cells were removed at 5 hr postinfection and cells were pulse-labeled in vivo. If inhibitors were introduced at or before infection, early viral proteins were synthesized only after a lag of 1-3 hr. However, if treatment was introduced 1 hr postinfection, reversion of the protein synthesis block was instantaneous. It appears that protein synthesis inhibitors reveal an in vivo translational block for viral mRNA. This block could be overcome by preinfection with a related virus. Furthermore, no block was observed in a virus-transformed human embryonic kidney cell line (293) which expresses early region 1 of the viral genome. Viral gene product(s) encoded in early region 1 may control translation of early adenovirus messenger RNA in vivo.

The same normal cell protein is phosphorylated after transformation by avian sarcoma viruses with unrelated transforming genes

The phosphorylation of a normal cellular protein of molecular weight 34,000 (34K) is enhanced in Rous sarcoma virus-transformed chicken embryo fibroblasts apparently as a direct consequence of the phosphotransferase activity of the Rous sarcoma virus-transforming protein pp60src. We have prepared anti-34K serum by using 34K purified from normal fibroblasts to confirm that the transformation-specific phosphorylation described previously occurs on a normal cellular protein and to further characterize the nature of the protein. In this communication, we also show that the phosphorylation of 34K is also increased in cells transformed by either Fujinami or PRCII sarcoma virus, two recently characterized avian sarcoma viruses whose transforming proteins, although distinct from pp60src, are also associated with phosphotransferase activity. Moreover, comparative fingerprinting of tryptic phosphopeptides shows that the major site of phosphorylation of 34K is the same in all three cases.

In vitro synthesis of adenovirus type 5 T antigens. I. Translation of early region 1-specific rna from lytically infected cells

Translation of early RNA specific for the leftmost early region 1 of adenovirus type 5 DNA in a rabbit reticulocyte cell-free system resulted in the synthesis of proteins with the following molecular weights: 65,000 (65K), 54K, 42 to 34K, 29K, 25K, 19K, and 18K. All of these proteins could be immunoprecipitated with hamster antitumor serum. The 42 to 34K proteins mapped in early region 1a, and those with molecular weights of 65K, 19K, and 18K mapped in early region 1b. The gene coding for the 54K protein may be localized outside of early region 1. We could not map unambiguously the 29K and 25K proteins. The identification of a 65K protein among products synthesized in vitro suggests that this protein may be identical to the 65K major T antigen present in adenovirus type 5-infected and -transformed cells, and this indicates that it is indeed encoded by the viral genome. This protein is encoded by a 23S mRNA. The other early region 1-specific proteins appear to be encoded by mRNA of approximately 13S, except for the 19K protein, which is synthesized with RNA sedimenting at both 13S and 23S.

Association of the src gene product of Rous sarcoma virus with cytoskeletal structures of chicken embryo fibroblasts

We have prepared cytoskeletons from normal and Rous sarcoma virus-transformed cells by extraction with nonionic detergents in a buffered salt solution designed to preserve the structure as it exists in vivo. Virtually all of the phosphoprotein pp60src in the cell is bound to such cytoskeletons. Furthermore, when these cytoskeletons are incubated in situ with [gamma-32P]ATP, pp60src is phosphorylated. Labeling of other apparently transformation-specific cytoskeletons phosphoproteins is also observed. These results directly demonstrate an association between pp60src and elements of the cytoskeleton and suggest that pp60src may exert at least some of its effects as a consequence of its interaction with this cellular framework.

Two tumor antigens and their polypeptides in adenovirus type 12-infected and transformed cells

A tumor (T) antigen, designated T antigen g, was visualized as fine fluorescent granules in nuclei of adenovirus type 12 (Ad12)-infected cells by immunofluorescence with sera from rats bearing HY cell tumors (H sera). HY cells are rat cells incompletely transformed by the Acc I-H endonuclease fragment (0-4.7 map units) of Ad12 DNA. The antigen is different from the usually described T antigen, designated T antigen f, which is visualized as fluorescent flecks or filaments in both nucleus and cytoplasm of Ad12-infected cells when tested with narrowly reacting T sera. Extracts of [(35)S]methioninelabeled infected cells were immunoprecipitated with H sera, and the resultant precipitate was analyzed by the two-dimensional gel electrophoresis technique of O'Farrell. The autoradiogram showed the presence of a cluster of several polypeptides (M(r) 35,000-40,000, pI 5.0-5.5) that was absent in extracts of mock-infected cells. A similar autoradiogram of infected cells analyzed with narrowly reacting T sera showed the presence of a small polypeptide (M(r) 10,000, pI 6.4), that was absent in extracts of mock-infected cells. The results show that M(r) 35,000-40,000 polypeptides are components of T antigen g and a M(r) 10,000 polypeptide is a component of T antigen f. Ad12-transformed cells showed a similar result. T antigen g was present and T antigen f was absent in HY cells. Both T antigen g and T antigen f were present in CY cells, which are rat cells completely transformed by the EcoRI-C endonuclease fragment (0-16 map units) of Ad12 DNA. The possible functions of these proteins are discussed.

Two low molecular weight peptides as common determinants to different molecular forms and specificities of hepatitis B e antigen (HBeAg)

Two fractions, I and II, corresponding to heavy and light molecular forms of HBeAg and respectively associated with the (HBe/1 + HBe/2) and (HBe/3) specificities, were separated by ammonium sulfate precipitation in HBeAg positive chimpanzee plasma. I 125-labeling of fractions I and II and immune precipitation by anti-HBe and anti-Human IgG were followed by autoradiographic analysis after SDS polyacrylamide gel electrophoresis: This revealed that two small peptides (a major 17,000 MW and minor 21,000 MW) seem common to the various molecular forms and specificities of HBeAg. Both peptides were found tightly linked to IgG in fraction I, associated with HBe/1 and HBe/2 and precipitated by 1.33 M (NH4)2SO4. In the HBe/3-positive fraction II these peptides seemed attached to IgG light chains only.

Tumor antigens of human Ad5 in transformed cells and in cells infected with transformation-defective host-range mutants

We have studied the polypeptides associated with the expression of the transforming region of the Ad5 genome by immunoprecipitating antigens (using the double antibody and protein A-Sepharose techniques) from cells infected with wild-type (wt) Ad5 or transformation-defective host range (hr) mutants and from cells transformed by Ad5. Three different antisera were used: P antiserum specific for early viral products (Russell et al., 1967) and two different hamster tumor antisera. Immunoprecipitation of antigens from wt-infected KB cells followed by SDS-polyacrylamide gel electrophoresis of precipitated proteins revealed that a major polypeptide having a molecular weight of approximately 58,000 was detected with all three antisera and with both the double antibody and the protein A-Sepharose techniques, while P antiserum also precipitated polypeptides of molecular weights 72,000, 67,000 and 44,000, which probably represent the DNA binding protein and related polypeptides, respectively. With the double antibody technique, in addition to the proteins mentioned above, P antiserum and the hamster tumor antisera precipitated a 10,500 dalton polypeptide which was not detected when the protein A-Sepharose procedure was used. Using either the double antibody or the protein A-Sepharose technique, we found that hr mutants from complementation group II failed to induce the synthesis of the 58,000 dalton protein, whereas mutants from complementation group I produced normal or near normal amounts. Using the double antibody technique, we found that the 10,500 dalton protein was absent or made in reduced amounts by group I mutants. A 58,000 dalton protein was detected in a number of different Ad5-transformed cell lines, including the 293 human line, the 14b hamster line and several transformed rat cell lines. This observation and the fact that transformation negative group II mutants fail to induce the synthesis of a 58,000 dalton polypeptide suggest that this protein is one of the Ad5-specific products necessary for cell transformation.

Immunofluorescence on avian sarcoma virus-transformed cells: localization of the src gene product

The localization of the avian sarcoma virus src gene product (termed p60src) was examined by indirect immunofluorescence in cells transformed by the Schmidt-Ruppin strain of Rous sarcoma virus, subgroup D (SR-RSV-D). Antiserum to p60src was obtained from rabbits bearing SR-RSV-D-induced tumors, and immunofluorescence was performed on chicken embryo fibroblasts (CEF) transformed with SR-RSV-D, as well as normal rat kidney (NRK) cells transformed by the same virus (termed SR-RK cells). Both acetone and formaldehyde fixation were used for the immunofluorescence tests. The specificity of the anti-tumor serum was first demonstrated in both cell systems by gel electrophoresis of immunoprecipitates prepared from 35S--methionine-labeled cells. Anti-tumor serum precipitated p60src from SR-RSV-D-transformed CEF but not from CEF infected with a transformation-defective mutant of SR-RSV-D. All viral structural proteins and precursors contained in these immunoprecipitates could be eliminated by competition with unlabeled virus. Similar experiments on SR-RK cells indicated that no viral proteins other than p60src were expressed in these cells, and this observation was supported by immunofluorescence tests using antiserum to whole virus. For immunofluorescence localization of p60src, reactions with viral structural proteins were blocked with unlabeled virus. This presaturation step, obligatory for p60src detection in the SR-RSV-D-transformed CEF, was unnecessary when antitumor serum was tested on SR-RK cells, since p60src was the only viral protein detectable in these cells. With acetone-fixed cells, p60src-specific immunofluorescence revealed a characteristic fluorescence pattern which was similar in both cell systems. The principal pattern was diffuse and situated in the cytoplasm. A clear nuclear fluorescence was never observed. Immunofluorescence on formaldehyde-fixed cells also indicated the cytoplasmic location of p60src and revealed a specific subcytoplasmic concentration of the fluorescence. With both fixation methods, an additional fluorescence pattern was seen between cells in contact, and was also found in both SR-RK cells and SR-RSV-D-transformed CEF. Immunofluorescence on viable cells suggested that p60src was not on the surface of these transformed cells. The fluorescence patterns were specific for avian sarcoma virus-transformed cells and were not found in uninfected cells, cells infected with a transformation-defective mutant of SR-RSV-D or cells transformed by an antigenically unrelated murine sarcoma virus. Furthermore, anti-tumor serum did not contain antibodies to proteins of the microtubules or intermediate filaments.

Comparative study by immunofluorescence of T and P antigens induced by adenovirus type 12 in permissive and nonpermissive cells

The development of adenovirus type 12 T antigen and of the complex of antigenic early proteins designated as P antigen was studied by immunofluorescence in productively infected KB cells and abortively infected RK-13 cells. T antigen is detected in both cell types very early in infection. In KB cells it presents the well known pattern of nuclear dots and flecks but in RK-13 cells at the time of maximum abundance, 18 hours p.i., T antigen forms a net of long filaments that fills the nucleus. Later, part of the filaments condense into a large aggregate that finally is apparently degraded. P antigen in infected RK-13 cells looks like T antigen in KB cells. In these cells, besides an early phase wherein P antigen is almost indistinguishable from T antigen, a late component is evident under the form of large balls and rosettes. The possible identification of this component with the DNA binding protein is discussed.