EFFICIENT HOMOLOGOUS RECOMBINATION OF TY1 ELEMENT CDNA WHEN INTEGRATION IS BLOCKED

Integration of the yeast retrotransposon Ty1 into the genome requires the self-encoded integrase (IN) protein and specific terminal nucleoti des present on full-length Ty1 cDNA. Ty1 mutants with defects in IN, t he conserved termini of Ty1 cDNA, or priming plus-strand DNA synthesis , however, were still able to efficiently insert into the genome when the elements were expressed from the GAL1 promoter present on a multic opy plasmid. As with normal transposition, formation of the exceptiona l insertions required an RNA intermediate, Ty1 reverse transcriptase, and Ty1 protease. In contrast to Ty1 transposition, at least 70% of th e chromosomal insertions consisted of complex multimeric Ty1 elements. Ty1 cDNA was transferred to the inducing plasmid as well as to the ge nome, acid transfer required the recombination and repair gene RAD52. Furthermore, multimeric insertions occurred without altering the level s of total Ty1 RNA, virus-like particle-associated RNA or cDNA, Ty1 ca psid proteins, or IN. These results suggest that Ty1 cDNA is utilized much more efficiently for homologous recombination when IN-mediated in tegration is blocked.