4 Yeast Transposable Elements

Abstract

I. INTRODUCTION
The transposons of yeast, Ty elements, are members of a widely distributed family of eukaryotic elements called long terminal repeat (LTR)-containing retrotransposons. Retrotransposons are organizationally and functionally similar to animal retroviruses. However, they differ in that they do not encode proteins analogous to the env gene products of retroviruses, and they replicate without an obligatory extracellular infection cycle (Fig. 1).

The yeast retrotransposons Ty1, Ty2, Ty3, and Ty4, discussed in this review, can be divided into two classes of elements widely represented among eukaryotic species. Ty1 and Ty2 are related to the copia class of plant and animal elements, whereas Ty3 is more closely related to the gypsy class of plant and animal elements and viruses. Ty4 has been discovered recently and seems to be more closely related to Ty1 and Ty2 than to Ty3 (R. Stucka et al., pers. comm.). The greater relatedness of these fungal elements to elements in plants and insects than to each other suggests that they may have moved into ancestors of their current hosts by horizontal transmission.

Yeast transposon biology has developed in exciting ways since the discovery of Ty1 10 years ago. This review summarizes those developments and attempts to highlight the ways in which yeast molecular genetics is now being applied to improve our understanding of retrotransposon transcription, replication, and integration. Further information on yeast Ty elements and retrotransposons from a variety of eukaryotes can be found in a number of books and review articles (Shapiro 1983; Varmus and Swanstrom...