Cell Cycle Control of Reverse Transcriptase Activity for the Yeast Retrotransposon Ty3

Abstract

Retroviruses and retrotransposons depend on their host cells to complete their replication cycles. In many cases, the viral step of reverse transcription is blocked when host cells are arrested in their cell cycle and this block is only released when the host cell resumes division. It has previously been shown that a retrotransposon found inSaccharomyces cerevisiae,Ty3, is unable to produce full-length double-stranded DNA, the product of reverse transcription, when the host cells are arrested in G1. In this study we show that, although Ty3 viruslike particles are produced at equivalent levels in arrested and nonarrested cells, the reverse transcriptase enzyme is inactive in arrested cells. The enzyme activity is restored when the arrested cells are permitted to resume cell division. These data suggest that a host factor regulates the activity of Ty3 reverse transcriptase in the cell cycle, which represents a novel cellular control of retroelements.