SILENT CHROMATIN DETERMINES TARGET PREFERENCE OF THE SACCHAROMYCES RETROTRANSPOSON TY5

The HML and HMR mating loci of Saccharomyces cerevisiae are bound in s ilent chromatin, which is assembled at the flanking E and I transcript ional silencers. The retrotransposon Ty5 preferentially integrates int o regions of silent chromatin, and Ty5 insertions near the HMR-E silen cer account for approximate to 2% of total transposition events. Most Ty5 insertions occur within 800 bp on either side of the autonomously replicating consensus sequence within HMR-E. Ty5 target preference is determined by silent chromatin, because integration near HMR-E is abol ished in strains with silencer mutations that alleviate transcriptiona l repression. The recognition of specific DNA sequences per se does no t direct integration, rather, it is the protein complex assembled at t he silencers. As demonstrated here for Ty5, recognition of specific ch romatin domains may be a general mechanism by which retrotransposons a nd retroviruses determine integration sites.