Ty1 and ty5 of saccharomyces cerevisiae

Ty1 and Ty5 of Saccharomyces cerevisiae are long terminal repeat (LTR) retrotransposons, members of a large and ubiquitous class of mobile genetic elements. Like the retroviruses, LTR retrotransposons replicate by reverse transcribing RNA into DNA and then integrating the DNA transposition intermediate into the genome of their host. This chapter begins with a description of Ty1 and Ty5, including their origins and genetic organization. Subsequent sections deal with four discrete steps in the LTR retrotransposon life cycle, namely, (i) transcription and transcriptional regulation; (ii) protein expression, processing, and virus-like particle assembly; (iii) reverse transcription; and (iv) integration. The study of activating mutations has unveiled a complex array of both positively and negatively acting factors responsible for Ty1's transcriptional regulation. The discussion of reverse transcription in the remainder of the chapter focuses on the native Ty1 enzyme. Negative post transcriptional regulation of Ty1 was suggested by the paradoxical observation that Ty1 mRNA is very abundant, yet mature Ty1 proteins are scarce and transposition infrequent. In the postgenomics era, S. cerevisiae is the proving ground for new technologies that are beginning to offer unprecedented insights into the complex regulatory and metabolic networks that underlie cellular biology. The development of the research tools and the accumulated knowledge that results from their use will undoubtedly greatly facilitate Ty1 and Ty5 research in the coming years.