Tryptic fingerprint analysis of adenovirus types 2, 5 and 12 DNA-Binding proteins

Human adenovirus 2 as immunogen in rabbits yields antisera with high titers of antibodies against the nonstructural 72K DNA-binding protein

Immunization in rabbits with intact, highly purified adenovirus type 2 (Ad2) virions, yielded antisera with high titers of antibodies against the 72 000 dalton DNA-binding protein (DBP). This was established by rocket immunoelectrophoresis when an anti-intact Ad2-antiserum was analyzed against fractions from an ion-exchange chromatogram of soluble antigens remaining after virus isolation from virus-infected HeLa cells. The high anti-DBP titer did not reflect the composition of the immunogen, since no DBP was detectable within virions. An antiserum raised in response to mildly disrupted virions showed no specificity against the DBP, but contained antibodies against the same structural proteins as the anti-intact Ad2-antiserum, when analyzed by the immunoblotting technique. These findings indicate that the nonpermissive rabbit as an experimental host permits early gene expression of a human adenovirus.

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

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

Structure and function of adenovirus DNA binding protein: comparison of the amino acid sequences of the Ad5 and Ad12 proteins derived from the nucleotide sequence of the corresponding genes

The adenoviral DNA binding protein (DBP) is a multifunctional protein involved in DNA replication and gene expression. In order to investigate the relation between structure and function of DBP, the amino acid sequences of the serotypes 5 and 12 (Ad5 and Ad12) have been compared. The amino acid sequence of Ad5 DBP was previously established by nucleotide sequence analysis of the Ad5 DBP gene (W. Kruijer, F. M. A. Van Schaik, and J. S. Sussenbach, Nucl. Acids Res. 9, 4439-4457, 1981). In this study the analysis of the Ad5 DBP gene and adjacent regions by determination of the sequence of the first leader in late DBP mRNA's and the splice point between the tripartite leader and the main body of the mRNA encoding the 100-kDa protein has been extended. The nucleotide sequence of the Ad12 DBP gene is also described. From the nucleotide sequence and RNA mapping data of Ad12 DBP mRNA's (I. Saito, J. Sato H. Handa, K. Shiraki, and H. Shimojo, Virology 114, 379-398, 1981) the complete Ad12 DBP amino acid sequence could be deduced. Ad12 DBP contains 484 amino acids and has an actual Mr of 54,992. It is 45 amino acids shorter than Ad5 DBP. Comparison of the Ad12 and Ad5 DBP amino acid sequences shows that several longer deletions are present in the N-terminal 125 amino acid residues of Ad12 DBP. In contrast, only a single amino acid deletion and insertion is found in the C-terminal 359 amino acids of Ad12 DBP. The N- and C-terminal domains of Ad12 and Ad5 DBP are 45 and 80% homologous, respectively. This suggests that both domains of DBP are subjected to different evolutionary pressures. Analysis of various Ad5 mutants with an altered DBP gene, has indicated that the C-terminal domain is involved in DNA replication and early gene expression, while the N-terminal domain has a role in late gene expression in monkey cells. These results are discussed in relation to the structure and function of adenovirus DBP.

In vitro complementation as an assay for purification of adenovirus DNA replication proteins

As an approach to the purification of adenovirus-encoded DNA replication proteins, we have developed in vitro complementation assays that make use of viral mutants defective in DNA replication in vivo. Nuclear extracts prepared from cells infected with H5ts36 or H5ts125, two such mutants belonging to different complementation groups, were found to be defective in viral DNA replication in vitro. However, replication activity could be restored by mixing the two extracts. Replication activity in either extract also could be restored by addition of appropriate replication-deficient fractions purified from cells infected with wild-type adenovirus. By using such assays, H5ts36- and H5ts125-complementing activities were extensively purified. As expected, purified H5ts125-complementing activity consisted of a single major polypeptide, the 72-kilodalton (kDal) adenovirus DNA binding protein. The purified H5ts36-complementing activity consisted of the 80-kDal adenovirus terminal protein precursor and two other major polypeptides with apparent molecular masses of 140 and 65 kDal. Formation of the 80-kDal terminal protein-dCMP complexes, the proposed initial step in adenovirus DNA replication, required components in the purified H5ts36-complementing fraction and a cellular factor(s) but did not require the adenovirus DNA binding protein. The complete in vitro adenovirus DNA replication reaction was reconstituted from the purified H5ts36-complementing activity, the adenovirus DNA binding protein, and an extract from uninfected cells.

Immunoautoradiographic detection of proteins after electrophoretic transfer from gels to diazo-paper: analysis of adenovirus encoded proteins

We describe a method by which complex protein mixtures are fractionated by standard one-dimensional Na-DodSO4/polyacrylamide gel electrophoresis or O'Farrell two-dimensional gel electrophoresis and then are efficiently and rapidly transferred electrophoretically to diazobenzyloxymethyl- or diazophenylthioether-paper and analyzed by immunoautoradiography. The method is illustrated with protein extracts of human KB cells infected with adenovirus type 2. Proteins were transferred from gels without decrease in resolution and with an increase in the sensitivity of detection by autoradiography when [35S]-methionine-labeled proteins were used. When unlabeled proteins were transferred, low levels of virus encoded proteins could be detected by sequential treatment of diazobenzyloxymethyl-paper with anti-adenovirus type 2 virion or anti-73,000 DNA binding protein and 125I-labeled Staphyloccus aureus protein A. Covalently bound viral proteins retained immunologic reactivity after dissociation of the protein A and antibody, By one-dimensional gel transfer/immunoautoradiography, seven virion proteins were detected as prominent bands and several others as weaker bands. By two-dimensional gel transfer/immunoautoradiography, several additional viral proteins were detected. By use of anti-DNA binding protein serum, the Mr 73,000 protein and Mr 41,000-48,000 subspecies were detected. A protein present at a concentration of approximately 1 part in 100,000 of the total protein can be identified in cell extracts. This method may be applicable to various biological problems requiring resolution and detection of small amounts of specific proteins that can be recognized immunologically or that can be detected by binding to specific radiolabeled DNA or RNA sequences or hormones.

Adenovirus-specific DNA-binding protein inhibits the hydrolysis of DNA by DNase in vitro

The adenovirus-specific DNA-binding protein was isolated from adenovirus type 5-infected KB cells and shown to possess DNase inhibitor activity. The protein decreased the rate of hydrolysis of single-strand DNA proportionately to its concentration in the reaction. Two peaks of activity were obtained upon sedimentation in a glycerol gradient, probably corresponding to the two major adenovirus-specific polypeptides in the preparation (molecular weights, 72,000 and 44,000). The DNase inhibitor activity of the adenovirus DNA-binding protein was distinguishable from that of the cellular DNA-binding protein, which we have described previously (K, Nass and G. D. Frenkel, J. Biol. Chem. 254:3407-3410, 1979), by its pattern of sedimentation and by the effect of temperature on the two activities. For the adenovirus DNA-binding protein, the ratio of DNase inhibitor activity at 43 degrees C to that at 30 degrees C was approximately 14, whereas for the cellular protein this ratio was less than 3. The DNase inhibitor activity with the temperature coefficient of 14 was absent from cells infected with adenovirus type 5 ts125 at 40 degrees C. DNase inhibition is a simple, sensitive, quantitative method for assay of the adenovirus DNA-binding protein.

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.

Purification and characterization of an early protein (E14K) from adenovirus type 2-infected cells

One adenovirus type 2 (Ad2) early protein, with an apparent molecular weight of 14,000 in sodium dodecyl sulfate-polyacrylamide gels (E14K), was purified to homogeneity. Purification involved fractionation of cytoplasmic extracts, precipitation at low pH, and DEAE-cellulose, phosphocellulose, and hydroxylapatite chromatography. The yield was around 12 microgram of purified protein per 10(9) HeLa cells. The two Ad2 DNA binding proteins with molecular weights of 75,000 and 45,000 (E75K and E45K) were purified by the same procedure. Tryptic peptide analyses indicated that the E14K protein is unrelated to the DNA binding proteins. The purified E14K protein has a high content of basic amino acids and a sedimentation coefficient of 5.5S in the native state, corresponding to a molecular weight of around 95,000. Pulse-chase experiments suggest that the E14K polypeptide is a primary translation product. Immunoprecipitation with a monospecific antiserum against the E14K protein revealed that it is exclusively localized in the cytoplasm of infected cells. E14K started to be synthesized at 2 hpostinfection, with a maximal rate of synthesis at 4 to 6 h postinfection. Immunoprecipitation of cell extracts from four different Ad2-transformed hamster embryo cell lines revealed that only one (Ad2HE4) of them expresses this protein. The adenovirus-simian virus 40 hybrid virus (Ad2ND1) does not express this protein, suggesting that the gene for the E14K protein is located in the part of the Ad2 genome which is deleted in this hybrid virus.

Adenovirus type 2 early proteins synthesized in vitro and in vivo: identification in infected cells of the 38,000- to 50,000- molecular-weight protein encoded by the left end of the adenovirus type 2 genome

Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of protein synthesized early after injection of human cells with adenovirus type 2 (Ad2) showed that polypeptides of 11,000 (11K), 12K, 14K, 15K, 19K, 21K, 24K, and 72k molecular weight were present in infected but not in mock-infected cells. These polypeptides corresponded in electrophoretic mobility to the following polypeptides synthesized in vitro by using mRNA complementary to specific regions of the Ad2 genome: 11K, 19K, 21K (91.5 to 96.8 map units), 14K (78.2 to 83.4 map units), 72K (62.4 to 67.9 map units), and 15K (4.9 to 11.0 map units). Polypeptides of 25K, 17K, 15.5K, and 13K were also synthesized in vitro, but have not yet been detected in infected cells. In addition, six adeno-specific polypeptides of 38 to 50K molecular weight could be discerned in infected cells if two-dimensional isoelectric focusing-polyacrylamide gel electrophoresis was used to compare extracts from infected and mock-infected cells. Partial protease digestion showed these 38 to 50K polypeptides to be related in sequence to each other and to the 40 to 50K polypeptide made in vitro (1.3 to 4.0 map units).

Adenovirus type 2 coded single-stranded DNA binding protein: in vivo phosphorylation and modification

The adenovirus type 2-coded single-stranded DNA binding protein (DBP) was shown to be a phosphoprotein and to exist in at least two forms that differ in mobility by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. After a 30-min pulse with [35S]methionine or 32PO4, 35S- or 32P-labeled DBP had a nominal molecular weight of 74,000 whereas after a 30-min label followed by a 20-h chase, 35S- and 32P-labeled DBP had a nominal molecular weight of 77,000. Both large and small forms of 35S- and 32P-labeled DBP bound to single-stranded DNA-cellulose columns and were eluted by 0.4 to 0.6 M NaCl; both forms also were immunoprecipitated by antiserum against adenovirus type 1-simian virus 40-induced tumor cells (this antiserum contains antibodies against DBP) and by monospecific antiserum against 95 to 99% purified DBP. With highly purified 32P-DBP labeled 7 to 10 h postinfection, it was shown that the 32P radioactivity was firmly associated with protein material (i.e., not contaminating nucleic acids or phospholipids) and had properties expected of a phosphoester of an amino acid; paper electrophoresis of acid hydrolysates of this preparation identified phosphoserine but not phosphothreonine. Phosphoserine but not phosphothreonine was also identified in acid hydrolysates of another preparation of 32P-DBP labeled for 30 min, chased for 20 h, and then immunoprecipitated by adenovirus type 1-simian virus 40 antiserum.