Translation of Pr55 gag Augments Packaging of Human Immunodeficiency Virus Type 1 RNA in a Cis -Acting Manner

Abstract

The full-length RNA of human immunodeficiency virus type 1 (HIV-1) serves both as a messenger (mRNA) to direct the translation of Pr55 ^gag proteins and as genomic or viral particle RNA (vpRNA) to be packaged into virions. In this study, we have assessed a putative cis-acting effect of Pr55 ^gag translation on HIV-1 RNA packaging. To pursue this subject, we have measured the relative competence of two distinct types of HIV-1 RNA for being packaged by virus particles under conditions in which only one of them is permissive for production of Pr55 ^gag . Not surprisingly, wild-type BH10 RNA was packaged at far higher efficiency than that associated with mutant viral RNA that was deleted of RNA packaging signals and incapable of Pr55 ^gag production. However, when production of Pr55 ^gag was eliminated from the wild-type BH10 viral RNA by insertion of stop codons either in matrix (MA) or in capsid (CA) sequences, regardless of retention of wild-type RNA packaging signals, these Pr55 ^gag -deficient viral RNAs were packaged at low levels similar to those observed with viral RNA species that lack RNA packaging signals and are capable of Pr55 ^gag generation. Moreover, loss of Pr55 ^gag production did not affect stability of the relevant viral RNA; this observation rules out the possibility that lowered packaging efficiency associated with Pr55 ^gag -deficient HIV-1 RNA is a result of reduced RNA stability. Taken together, our data demonstrate that cis translation of Pr55 ^gag is needed for efficient packaging of HIV-1 RNA.