Induction of yeast Ty element transcription by ultraviolet light

Abstract

Gene expression induced in response to DNA damage is now well characterized in Escherichia coli (reviewed in ref. 1), and the functions of the proteins encoded by some of these genes are also understood. Physiological evidence has implicated similar responses in eukaryotes^2–9, and recently DNA sequences whose transcription can be induced by ultraviolet (UV) irradiation have been identified and cloned from the yeast Saccharomyces cerevisiae^l0–12. With the exception of the Ustilago maydis Recl protein, however¹³, no inducible eukaryotic proteins have been characterized with respect to their role in post-irradiation DNA metabolism. Using differential colony hybridization methods, we have described the cloning of four S. cerevisiae DNA sequences whose transcript levels increase ∼10-fold after a dose of UV irradiation which was previously shown to induce two novel proteins in yeast^12,14. Although they possess different restriction enzyme maps, these sequences did share elements of homology as defined by cross-hybridization experiments. We show here that all four sequences possess homology with yeast Ty elements. These elements comprise a family of heterogeneous, dispersed and moderately repetitive transposable DNA sequences which are present as ∼30 copies per haploid genome in laboratory strains and whose archetypal structure is shown in Fig. 1 (refs 15,16 and reviewed in ref. 17). We also show directly that the 5.7-kilobase (kb) major Ty transcript, initiated in one terminal direct repeat sequence (δ) and terminated in the other¹⁸, is induced by UV irradiation.