Induction of yeast DNA ligase genes in exponential and stationary phase cultures in response to DNA damaging agents

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Abstract
Summary UV-irradiation of stationary phase cells of Saccharomyces cerevisiae and Schizosaccharomyces pombe leads to a 9-fold and 90-fold increase in transcript levels from the respective DNA ligase genes CDC9 and CDC17, whereas exponential cells show only 3-fold and 2-fold increases. Induction of CDC9 after MMS treatment and γ-irradiation was also observed by using a CDC9-lacZ translational fusion and assaying for β-galactosidase. Surprisingly, irradiation of S. cerevisiae induces only a 50% increase in DNA ligase itself, probably reflecting the extremely high in vivo stability of the enzyme. The UV-induction of ligase may be part of a “fail-safe” mechanism which, together with the enzyme stability, ensures adequate supplies of this essential enzyme.