The Saccharomyces cerevisiae DNA recombination and repair functions of theRAD52 epistasis group inhibit Tyl transposition

RNA transcribed from the Saccharomyces cerevisiae retrotransposon Ty1 accum ulates to a high level in mitotically growing haploid cells, yet transposit ion occurs at very low frequencies. The product of reverse transcription is a linear double-stranded DNA molecule that reenters the genome by either T y1-integrase-mediated insertion or homologous recombination with one of the preexisting genomic Ty1 (or delta) elements. Here we examine the role of t he cellular homologous recombination functions on Ty1 transposition. We fin d that transposition is elevated in cells mutated for genes in the RAD52 re combinational repair pathway, such as RAD50, RAD51, RAD52 RAD54, or RAD57, or in the DNA ligase I gene CDC9, but is not elevated in cells mutated in t he DNA repair functions encoded by the RAD1, RAD2, or MSH2 genes. The incre ase in Ty1 transposition observed when genes in the RAD52 recombinational p athway are mutated is not associated with a significant increase in Ty1 RNA or proteins. However, unincorporated Ty1 cDNA levels are markedly elevated . These results suggest that members of the RAD52 recombinational repair pa thway inhibit Ty1 post-translationally by influencing the fate of Ty1 cDNA.