The role of yeast DNA 3'-phosphatase Tpp1 and rad1/Rad10 endonuclease in processing spontaneous and induced base lesions.
Tpp1 is a DNA 3'-phosphatase in Saccharomyces cerevisiae that is believed to act during strand break repair. It is homologous to one domain of mammalian polynucleotide kinase/3'-phosphatase. Unlike in yeast, we found that Tpp1 could confer resistance to methylmethane sulfonate when expressed in bacteria that lack abasic endonuclease/3'-phosphodiesterase function. This species difference was due to the absence of delta-lyase activity in S. cerevisiae, since expression of bacterial Fpg conferred Tpp1-dependent resistance to methylmethane sulfonate in yeast lacking the abasic endonucleases Apn1 and Apn2. In contrast, beta-only lyases increased methylmethane sulfonate sensitivity independently of Tpp1, which was explained by the inability of Tpp1 to cleave 3' alpha,beta-unsaturated aldehydes. In parallel experiments, mutations of TPP1 and RAD1, encoding part of the Rad1/Rad10 3'-flap endonuclease, caused synthetic growth defects in yeast strains lacking Apn1. In contrast, Fpg expression led to a partial rescue of apn1 apn2 rad1 synthetic lethality by converting lesions into Tpp1-cleavable 3'-phosphates. The collected experiments reveal a profound toxicity of strand breaks with irreparable 3' blocking lesions, and extend the function of the Rad1/Rad10 salvage pathway to 3'-phosphates. They further demonstrate a role for Tpp1 in repairing endogenously created 3'-phosphates. The source of these phosphates remains enigmatic, however, because apn1 tpp1 rad1 slow growth could be correlated with neither the presence of a yeast delta-lyase, the activity of the 3'-phosphate-generating enzyme Tdp1, nor levels of endogenous oxidation.
SciCrunch is a data sharing and display platform. Anyone can create a custom portal where they can select searchable subsets of hundreds of data sources, brand their web pages and create their community. SciCrunch will push data updates automatically to all portals on a weekly basis. User communities can also add their own data to scicrunch, however this is not currently a free service.