Regulation of Ty Element Transposition in Saccharomyces cerevisiae: Isolation and Initial Characterization of RTT Mutants

Abstract

The yeast retrotransposon Ty1 has been tagged with a reporter gene that allows single-step selection of RNA-mediated transposition events. The reporter gene is the yeast HIS3 gene interrupted by an artificial intron (Al) in the antisense orientation. This his3AI gene is inserted into a Ty1 element such that His⁺ cells arise from splicing and retrotransposition of the marked Ty1 transcript. By mutagenizing closely related MATa and MATα strains containing genomic Ty1 elements marked with his3AI, 143 putative "hypertransposition" mutants (designated Regulator of Ty Transposition, RTT) were isolated by screening for an elevated level of His⁺ papillation. The mutants were divided into two groups based on northern analysis; 47 mutants showed increased Ty1 RNA levels, while 96 mutants showed no increase in Ty1 RNA levels. Forty-two mutants did not exhibit an increased level of splicing of the Ty1mhis3AI transcript. One mutant, rtt46B, showed a modest increase in splicing of the marked Ty1 transcript. In 38 of 69 mutants analyzed by tetrad dissection, the rtt mutation segregated as a single genetic locus. Two recessive mutants with unique secondary phenotypes, rtt822A and rtt13AH, were selected for further characterization. Mutant rtt13AH showed an increase in the level of Ty1 transposition at a specific target locus. The results indicate that this mutant collection will identify important genes responsible for regulating Ty1 transposition.