Transcriptional regulation of MAG1 and DDI1 in response to DNA damage.

摘要

In response to DNA damage, both prokaryotic and eukaryotic cells activate stress responses that result in specific alterations in patterns of gene expression and an active inhibition of cell division. In all eukaryotic organisms, it is suggested that the cellular response to DNA damage is coordinated by the DNA damage checkpoint. In the budding yeast Saccharomyces cerevisiae , a dozen of DNA damage checkpoint genes have been identified. These genes encode components of signal transduction cascades that consist of sensors, transducers and downstream effectors.;In order to elucidate the mechanism of transcriptional regulation in response to DNA damage, the expression of two DNA damage inducible genes, MAG1 and DDI1, was studied. MAG1 encodes a 3-methyladenine DNA glycosylase, the first enzyme in a multi-step base-excision-repair pathway for the removal of lethal lesions such as 3-methyladenine and protects yeast cells from killing by DNA methylating agents such as methyl methanesulphonate (MMS). DDI1 was identified immediately upstream of, and shares promoter sequences with MAG1. Despite their coordinated expression patterns in response to DNA damage, differential regulation was previously observed in a dun1 mutant and in the presence of cycloheximide. Indeed, in addition to a shared UAS DM element, MAG1 and DDI1 contain unique cis-acting regulatory elements. In this study, three hypotheses were tested: (1) MAG1 and DDI1 are differentially regulated by DNA damage checkpoint through different signal transduction pathways; (2) an interaction between a trans-acting transcriptional activator and UASDM is required for the basal-level and DNA damage induction of both MAG1 and DDI1 genes; and (3) one or more DNA repair proteins may play a role in the DNA damage transcriptional regulation by sensing DNA damage and interacting with checkpoint components.;Through genetic analyses, it was found that G1/S and G2/M checkpoint genes do not play a significant role in the MAG1 and DDI1 expression. In contrast, MAG1 is controlled by the MEC1-RAD53-DUN1 pathway, whereas DDI1 is controlled by two parallel signal transduction pathways represented by MEC1-RAD53-DUN1 and CHK1-PDS1.;Using the UASDM element as bait for one-hybrid library screening, PDR3 was isolated, whose product is a transcriptional activator in the pleiotropic drug resistance pathway, and it was demonstrated that Pdr3 specifically regulates the MAG1/ DDI1 damage induction by binding UASDM. (Abstract shortened by UMI.).