Local definition of Tyl target preference by long terminal repeats and clustered tRNA genes

LTR-containing retrotransposons reverse transcribe their RNA genomes, and the resulting cDNAs are integrated into the genome by the element-encoded integrase protein. The yeast LTR retrotransposon Ty1 preferentially integrates into a target window upstream of tDNAs (tRNA genes) in the yeast genorne. We investigated the nature of these insertions and the target window oil a genomic scale by analyzing several hundred de novo insertions upstream of tDNAs in two different multicopy gene families. The pattern of insertion upstream of tDNAs was nonrandom and periodic, with peaks separated by similar to80 bp. Insertions were not distributed equally throughout the genome, as certain tDNAs within a given family received higher frequencies of upstream Ty1 insertions than others. We showed that the presence and relative position of additional tDNAs and LTRs surrounding the target tDNA dramatically influenced the frequency of insertion events upstream of that target.