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Two proteolytic pathways regulate DNA repair by cotargeting the Mgt1 alkylguanine transferase SCIE SCOPUS

Title
Two proteolytic pathways regulate DNA repair by cotargeting the Mgt1 alkylguanine transferase
Authors
Hwang, CSShemorry, AVarshavsky, A
Date Issued
2009-02-17
Publisher
National Academy of Science
Abstract
O-6-methylguanine (O(6)meG) and related modifications of guanine in double-stranded DNA are functionally severe lesions that can be produced by many alkylating agents, including N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), a potent carcinogen. O(6)meG is repaired through its demethylation by the O-6-alkylguanine-DNA alkyltransferase (AGT). This protein is called Mgmt (or MGMT) in mammals and Mgt1 in the yeast Saccharomyces cerevisiae. AGT proteins remove methyl and other alkyl groups from an alkylated O-6 in guanine by transferring the adduct to an active-site cysteine residue. The resulting S-alkyl-Cys of AGT is not restored back to Cys, so repair proteins of this kind can act only once. We report here that S. cerevisiae Mgt1 is cotargeted for degradation, through a degron near its N terminus, by 2 ubiquitin-mediated proteolytic systems, the Ubr1/Rad6-dependent N-end rule pathway and the Ufd4/Ubc4-dependent ubiquitin fusion degradation (UFD) pathway. The cotargeting of Mgt1 by these pathways is synergistic, in that it increases not only the yield of polyubiquitylated Mgt1, but also the processivity of polyubiquitylation. The N-end rule and UFD pathways comediate both the constitutive and MNNG-accelerated degradation of Mgt1. Yeast cells lacking the Ubr1 and Ufd4 ubiquitin ligases were hyperresistant to MNNG but hypersensitive to the toxicity of overexpressed Mgt1. We consider ramifications of this discovery for the control of DNA repair and mechanisms of substrate targeting by the ubiquitin system.
URI
https://oasis.postech.ac.kr/handle/2014.oak/12749
DOI
10.1073/pnas.0812316106
ISSN
0027-8424
Article Type
Article
Citation
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, vol. 106, no. 7, page. 2141 - 2147, 2009-02-17
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황철상HWANG, CHEOL SANG
Dept of Life Sciences
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