title: Impaired cleavage of the joint gag-pol polyprotein precursor and virion assembly in a temperature-sensitive mutant of Rous sarcoma virus.
abstract: A temperature-sensitive coordinate mutant tsLA83 of Prague (PR-B) strain of Rous sarcoma virus at the nonpermissive temperature (41 degrees) produces noninfectious virus particles (NI-LA83) which contained only 3% of the reverse-transcriptase activity present in infectious virions. Analyses of [35S]methionine-labeled NI-LA83 showed the presence of all of the viral proteins except reverse transcriptase. Pulse-chase analyses of the virus-specified proteins in cells infected with LA83 or PR-B showed that the gag and glycoprotein precursors, Pr76gag and gPr95env, respectively, were processed at both 35 and 41 degrees. The reverse-transcriptase precursor, Pr180gag-pol, however, was not processed in LA83-infected cells at 41 degrees. In contrast, cells infected with LA83 or PR-B at 35 degrees as well as with PR-B at 41 degrees showed normal cleavage of Pr180gag-pol. A shiftdown of LA83-infected cells at 41 degrees to the permissive temperature 35 degrees resulted in the normal processing of Pr180gag-pol and production of infectious virus containing reverse transcriptase. Electron microscopic analysis showed that at 41 degrees cells infected with LA83 showed a large number of budding structures but fewer released particles. A shiftdown from 41 to 35 degrees resulted in an increase of virus particles with a concomitant decrease in budding structures suggesting that the processing of reverse-transcriptase precursor is related to virion assembly.
mesh_terms: D000818:Animals; D000956:Antigens, Viral / Q000235:genetics*; D001358:Avian Sarcoma Viruses / Q000235:genetics* / Q000648:ultrastructure; D002478:Cells, Cultured; D002642:Chick Embryo; D005347:Fibroblasts / Q000648:ultrastructure; D015683:Gene Products, gag; D007700:Kinetics; D008854:Microscopy, Electron; D009154:Mutation; D010446:Peptide Fragments / Q000032:analysis; D011498:Protein Precursors / Q000235:genetics*; D013696:Temperature; D014764:Viral Proteins / Q000235:genetics*; D014771:Virion / Q000235:genetics* / Q000648:ultrastructure
chemical_list: D000956:Antigens, Viral; D015683:Gene Products, gag; D010446:Peptide Fragments; D011498:Protein Precursors; D014764:Viral Proteins