Translation of Pr55gagAugments Packaging of Human Immunodeficiency Virus Type 1 RNA in aCis-Acting Manner

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Abstract
The full-length RNA of human immunodeficiency virus type 1 (HIV-1) serves both as a messenger (mRNA) to direct the translation of Pr55gag 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 Pr55gag 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 Pr55gag. 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 Pr55gag production. However, when production of Pr55gag 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 Pr55gag-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 Pr55gag generation. Moreover, loss of Pr55gag production did not affect stability of the relevant viral RNA; this observation rules out the possibility that lowered packaging efficiency associated with Pr55gag-deficient HIV-1 RNA is a result of reduced RNA stability. Taken together, our data demonstrate that cis translation of Pr55gag is needed for efficient packaging of HIV-1 RNA.

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