Characterization of the DNA repair role of the Saccharomyces cerevisiae NSE1 gene

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Title: Characterization of the DNA repair role of the Saccharomyces cerevisiae NSE1 gene
Author: Sergio Renan Santa Maria Guerra
Abstract: In eukaryotes , the structural maintenance of chromosomes (SMC ) complexes play important roles in chromosome dynamics . The Saccharomyces cerevisiae Smc5 -Smc6 complex is composed of eight essential subunits and is particularly required for a normal response to DNA damage . Hypomorphic mutations in these subunits render cells sensitive to DNA damaging agents . Of the non -SMC subunits , Nse1 and Mms21 are of particular interest , because Nse1 contains a RING finger motif characteristic of ubiquitin ligases and Mms21 is a SUMO ligase that sumoylates different subunits of the complex and also other DNA repair proteins . \r \nIn this study , we have isolated a mutation , nse1 -101 , which results in sensitivity to UV irradiation and MMS . We used this mutant for genetic and postreplication repair (PRR ) experiments to examine the role of Nse1 in promoting the bypass of DNA lesions . From epistasis analyses , we inferred a role for Nse1 in the Rad52 -dependent repair pathway . Our PRR experiments further support our genetic results , as the newly synthesized DNA does not attain the normal size in UV irradiated nse1 -101 cells . On the basis of these and other studies we have provided evidence for the role of Nse1 in the PRR of UV -damaged DNA in a Rad5 -independent but Rad52 -dependent manner . \r \nWe also constructed mutations in the RING domains of Nse1 and Mms21 to investigate the role of their ligase functions in DNA repair . As was observed with nse1 -101 , epistasis analyses with the nse1 and mms21 RING mutants also suggest a role for their ligase activities in Rad52 -dependent PRR . As this pathway has been suggested to promote PRR when the lesion is on the lagging strand , our studies have indicated a role for Nse1 and Mms21 in promoting PRR on the lagging strand together with the proteins of the Rad52 group . We propose that the Smc5 -Smc6 complex functions in this pathway by holding the DNA duplexes in close proximity using the ring structure formed by the Smc5 -Smc6 dimer . Further , the ubiquitin ligase and SUMO ligase functions of Nse1 and Mms21 , respectively , can contribute to this process by mediating physical interactions between the Smc5 -Smc6 complex and the Rad52 group of recombinational proteins .
URI: http : / /hdl .handle .net /2152 .3 /111
Date: 2008-05-14

Citation

Characterization of the DNA repair role of the Saccharomyces cerevisiae NSE1 gene. Doctoral dissertation, The University of Texas Medical Branch. Available electronically from http : / /hdl .handle .net /2152 .3 /111 .

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