TRANSLATION OF BOVINE LEUKEMIA-VIRUS VIRION RNAS IN HETEROLOGOUS PROTEIN-SYNTHESIZING SYSTEMS

Bovine leukemia virus 60-70S RNA was heat denatured, the poly(A)-containing species were separated by velocity sedimentation and several size classes were translated in a micrococcal nuclease-treated cell-free system from rabbit reticulocytes. The major RNA species sedimented at 38S and migrated as a single component of MW 2.95 .times. 106 when analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The predominant polypeptides of the in vitro translation of bovine leukemia virus 38S RNA were products with MW of 70,000 and 45,000; minor components with MW of 145,000 and 18,000 were also observed. Two lines of evidence indicate that the 70,000- and 45,000 MW polypeptides represent translation products of the gag gene of the bovine leukemia virus genome (Pr70gag and Pr45gag). They are specifically precipitated by a monospecific antiserum to the major internal protein, p24 and they are synthesized and correctly processed into virion proteins p24, p15 and p10 in Xenopus laevis oocytes microinjected with bovine leukemia virus 38S RNA. The 145,000 MW polypeptide was immunoprecipitated by the anti-p24 serum and not by an antiserum to the major envelope glycoprotein, gp60. It contained all the tryptic peptides of Pr70gag and additional peptides unique to it, and thus represents an elongation product of Pr70gag in an adjacent gene, presumably the pol gene. The 18,000 MW product was antigenically unrelated to p24 and gp60 and shared no peptides in common with Prgag, Pr45gag or the 145,000 MW polypeptide. It was maximally synthesized on a poly(A)-containing virion 16-18S RNA, and evidence is presented that this RNA is a 3'' end-derived subgenomic fragment of the bovine leukemia virus genome rather than a contaminating cellular RNA.