Movement of yeast transposable elements by gene conversion.

We have constructed yeast strains in which Ty (transposon yeast) elements at the HIS4 locus are genetically marked with the yeast URA3 gene. By isolating and analyzing Ura- derivatives of these strains, we have detected a variety of Ty-mediated recombination events. In this paper, we describe events in which the DNA sequence of the Ty element at the HIS4 locus is replaced by the DNA sequence of a different Ty element. These replacements occur without alterations in the flanking DNA sequence and without chromosomal aberrations. We believe that these events result from gene conversion between the Ty element at HIS4 and a Ty element at a different site in the yeast genome. Gene conversion can occur between Ty elements that differ by large insertion and substitution mutations. These recombination events result not only in the movement of Ty sequences but also in alterations in expression of the adjacent HIS4 gene. Different Ty elements at the same site in the HIS4 regulatory region can result in His-, His+, and cold-sensitive His+ phenotypes. Several Ty elements render expression of the HIS4 gene subject to control by genes at the mating type locus.