Characterization of Rous sarcoma virus src gene products synthesized in vitro

Abstract

The cell-free synthesis of 3 major proteins from virion RNA of nondefective Rous sarcoma virus (RSV), but not from RNA of transformation-defective deletion mutants, was observed. The apparent MW of these transformation-specific proteins are approximately 60,000 (60K), 25K and 17K. Tryptic maps of methionine-containing peptides revealed the 17K, 25K and 60K proteins to be overlapping in sequence. Only partial homology was observed between the 17K, 25K and 60K proteins synthesized from Schmidt-Ruppin strain, subgroup D, RSV RNA and those synthesized from Prague strain, subgroup B, RSV RNA. About half of the methionine peptides in the Schmidt-Ruppin strain, subgroup D, 60K protein were shared with the Prague strain, subsgroup D, 60K protein and the rest were distinct to each. The virion RNA coding for the 60K, 25K and 17K proteins were polyadenylated and sedimented with maximal mRNA activity at about 23, 19-20 and 18S, respectively. In addition, transformation-specific proteins with MW of 39K and 33K were observed by in vitro synthesis. These proteins are also related to the 60K, 25K and 17K proteins and were synthesized from polyadenylated RSV RNA of approximately 21-22S. RNase T1-resistant oligonucleotides were analyzed in parallel, and the src-specific oligonucleotides were first present in equimolar amounts in those gradient fractions sedimenting at 21-22S. Synthesis of the 60K protein is probably initiated near the 5'' terminus of the src gene, but the 39K, 33K, 25K and 17K proteins are initiated internally in the src gene. These proteins appear to be initiated independently, but they may have a common termination site.