Effect of polymerase mutations on packaging of primer tRNAPro during murine leukemia virus assembly

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Abstract
The role of reverse transcriptase in selective encapsidation of the murine leukemia virus (MuLV) tRNA primer, tRNAPro, was investigated by examining the tRNA composition of several nonconditional pol mutants. One mutant, clone 23, which contains an altered polymerase about 40% smaller than the wild-type enzyme had a typical viral tRNA pattern, including normal levels of tRNAPro in free and 70S-associated 4S RNA. Another class of mutants, produced by Moloney murine leukemia virus-infected cell clone M13 and subclone M13/1, did not contain any detectable polymerase protein and had reduced amounts of tRNAPro in free 4S RNA. The level of tRNAPro associated with the genome was normal in the mutant virions. The reverse transcriptase protein may be involved in the initial selection of tRNA primer during virus assembly but not in the subsequent association of this tRNA with genomic RNA.