Characterization of a normal avian cell protein related to the avian sarcoma virus transforming gene product.

In this paper, we identify and characterize both structurally and functionally a protein from normal uninfected avian cells that is antigenically related to the pp60^src viral protein responsible for transformation by ASV. This protein was detected by immunoprecipitation of radiolabeled normal cell extracts with serum derived from marmosets bearing ASV-induced tumors. The normal avian cell protein, which has been detected in each of the four avian species tested (chicken, duck, quail and pheasant) is a phosphoprotein of 60,000 daltons. This protein is not related to any of the ASV structural proteins; however, its immunoprecipitation is prevented by preadsorption of the antiserum with cell extracts specifically containing pp60^src. Peptide analyses by partial proteolysis using chymotrypsin resulted in a map of the normal cell protein that was very similar to that of pp60^src. When Staphylococcus aureus V8 protease was used, however, one of the major cleavage products of the normal cell protein exhibited an altered migration with respect to the corresponding pp60^src product. Tryptic phosphopeptide analyses demonstrated that phosphorylation of the normal cell protein was also different from that seen in pp60^src. The expression of the normal cell protein did not seem to be affected by cellular growth conditions, maintaining a constant level which was approximately 30–50 fold lower than that of pp60^src in infected cells. The normal cell protein appeared to be functionally dissimilar to pp60^src lacking detectable protein kinase activity in the currently available assay system.     

Dipeptide backbone conformation and antibody recognition of a viral octapeptide epitope.

The peptide YKGTMDSG (Tyr-Lys-Gly-Thr-Met-Asp-Ser-Gly) represents an important antigenic determinant from the glycoprotein G2 of the pathogenic Rift Valley fever virus. By preparing a series of single-residue substitution peptides, the importance to antigenicity of individual residues within this octapeptide has been determined. Here, we investigated a simple and rapid computational analysis to test for correlations between the observed antigenicity of the substitution analogue peptides and the calculated conformational preferences in local regions of the peptides. Conformational energy analyses were carried out on all dipeptide combinations represented in the wild-type octapeptide and in the single-residue substitution analogue peptides. Conformational similarities and differences between wild-type and substitution dipeptide pairs were determined. The results of these computational analyses were then compared with the data on the relative antigenicity of the wild-type octapeptide and the substitution analogues. This comparison revealed a positive correlation. Substitution peptides showing changes in antigenicity possessed significant changes in the calculated backbone conformation relative to wild type in the dipeptides encompassing the residue substitution. Substitution peptides showing no change in antigenicity similarly showed no significant changes in dipeptide conformation. The potential utility of dipeptide conformational energy analyses and this preliminary structure-activity correlation are discussed.     

Elimination of residual RNase activity from purified preparations of RNA-directed DNA polymerase.

Preparations of RNA-directed DNA polymerase purified from RNA tumor viruses by standard methods generally contain trace amounts of single-stranded RNA endonucleolytic activity detectable only by relatively sensitive methods. This contaminating RNase activity has been found to be completely inhibited when RNA-directed DNA polymerase reactions are carried out in the presence of low concentrations of bentonite. Under these conditions, only minimal inhibition of the DNA polymerase and RNase H activities of the RNA-directed DNA polymerase was observed.     

In vitro transcription of 70S RNA by the RNA-directed DNA polymerase of Rouse sarcoma virus: lack of influence of RNase H.

The influence of Rous sarcoma virus (RSV)-associated RNase H on the in vitro synthesis of DNA by the RSV RNA-directed DNA polymerase was determined under conditions whereby RNase H activity was selectively inhibited with NaF. Not only were we unable to detect any effect on the size, structure, or genetic complixity of the DNA product synthesized in the absence of RNase H activity, but the displacement of DNA from the 70S RNA:DNA hybrid structures was also unaffected. The suitability of 70S RNA:DNA hybrid structures synthesized in vitro to serve as a substrate for RNase H is discussed.     

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.