ABSTRACT
The first transposable element found in Saccharomyces cerevisiae was called Ty. The use of Ty element marked by insertion of appropriate sequences, such as a functional URA 3 gene, allowed the detection of frequent conversion events. An important step forward was made by replacing the promoter of a Ty H3 element with the GAL1 promoter. In order to follow accurately the fate of the Ty H3 element, it was marked by the insertion of a 40-bp synthetic lac O segment, near the 3' end of the element. The presence of viruslike particles and reverse transcriptase in transposition-induced cells suggests a strong analogy between Ty elements and retroviruses. Ty elements contain a sequence that could serve as a tRNA primer binding site, adjacent to the 5' LTR and an oligopurine tract, which could prime second-strand synthesis, adjacent to the 3' LTR.
