A single amino acid change in the yeast retrotransposon Ty5 abolishes targeting to silent chromatin

Many retrotransposons and retroviruses are thought to select integration sites through interactions with specific chromosomal proteins. In yeast, the Ty5 retrotransposon integrates preferentially within regions bound by silent chromatin, namely the telomeres and the HMR and HML mating loci. A Ty5 mutant (M3) was identified with an approximately 20-fold decrease in targeted integration as measured by a plasmid-based targeting assay. Of ten chromosomal insertions generated by M3, none were located at the telomeres or silent mating loci. A single amino acid change at the boundary of integrase and reverse transcriptase is responsible for the mutant phenotype. We predict that this mutation lies within a targeting domain that mediates Ty5 target choice by interacting with a component of silent chromatin.