RNA-mediated recombination in S. cerevisiae.

The existence of pseudogenes and the observation of intron loss suggest that RNA can serve as an intermediate in recombination. We used a HIS3 reporter gene to show that RNA-mediated recombination occurs in yeast. His3+ prototroph formation required transcription and expression of the retrotransposon Ty. Two RNA-mediated recombination events were detected: homologous recombination between the cDNA and plasmid his3 sequences, resulting in intron loss, and insertion of the cDNA into the chromosome in the absence of HIS3 homology. The chromosomal His3+ prototrophs showed many hallmarks of naturally occurring pseudogenes. They integrated at novel sites in the chromosome, lacked introns, and possessed poly(A) tracts. Additionally, their 5' ends corresponded with the site of initiation of the GAL1 transcript.