The Mutation Rate of Human Immunodeficiency Virus Type 1 Is Influenced by thevprGene

Abstract

A system has been designed to study thein vivoforward rate of mutation of human immunodeficiency virus type 1 (HIV-1) during one round of replication. A HIV-1 shuttle vector was used that contained thelacZα peptide gene as a reporter for mutations. The forward mutation rate of HIV-1 was found to be 3 × 10−5mutations per target base pair per cycle, or about 20-fold lower than the error rates reported for purified HIV-1 reverse transcriptase with sense-strand RNA and DNA templates of thelacZα peptide gene in a cell-free system. To test the hypothesis that thevprgene product might, at least in part, account for the lower mutation rate observedin vivo,a HIV-1 vector was replicated to determine if the mutation rate was higher in the absence of the wild-typevprgene product. Avpr−shuttle vector had an overall mutation rate as much as 4-fold higher than that of the parental vector. A shuttle vector with an amino acid substitution in Vpr that prevents efficient incorporation of Vpr into virus particles was found to have a mutation frequency similar to that of thevpr−vector, and was interpreted to indicate a requirement for Vpr incorporation into the virus particle in order to observe the influence ofvpron the mutation rate. Replication of avpr−shuttle vector in the presence of a wild-typevprexpression plasmid led to a mutation frequency similar to that of the parental vector, suggesting that thevprmutation could be complementedin trans.Immunoprecipitation analysis indicated that Vpr virion incorporation coincided with the influence ofvpron the mutation rate.