Increase in Ty1 cDNA recombination in yeast sir4 mutant strains at high temperature

Transposition of the Ty1 element of the yeast Saccharomyces cerevisiae is temperature sensitive. We have identified a null allele of the silent information regulator gene SIR4 as a host mutant that allows for transposition at high temperature. We show that the apparent increase in transposition activity in sir4 mutant strains at high temperature is dependent on the RAD52 gene and is thus likely resulting from an increase in Ty1 cDNA recombination, rather than in IN-mediated integration. General cellular recombination is not increased at high temperature, suggesting that the increase in recombination at high temperature in sir4 mutants is specific for Ty1 cDNA. Additionally, this high-temperature Ty1 recombination was found to be dependent on functional Sir2p and Sir3p. We speculate that the increase in recombination seen in sir4 mutants at high temperature may be due to changes in chromatin structure or Ty1 interactions with chromosomal structures resulting in higher recombination rates.