Journal
NUCLEIC ACIDS RESEARCH
Volume 37, Issue 6, Pages 2026-2036Publisher
OXFORD UNIV PRESS
DOI: 10.1093/nar/gkp038
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Funding
- National Institutes of Health [T32 GM007377, GM58015]
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The DNA structure-selective endonuclease Mus81-Mms4/Eme1 incises a number of nicked joint molecule substrates in vitro. 3-flaps are an excellent in vitro substrate for Mus81-Mms4/Eme1. Mutants in MUS81 are synthetically lethal with mutations in the 5-flap endonuclease FEN1/Rad27 in Saccharomyces cerevisiae and Schizosaccharomyces pombe. Considering the possibility for isoenergetic interconversion between 3- and 5- flaps, these data are consistent with the hypothesis that Mus81-Mms4/Eme1 acts on 3-flaps in vivo. FEN1/Rad27 prefers dually flapped substrates and cleaves in a way that allows direct ligation of the resulting nick in the product duplex. Here we test the activity of Mus81-Mms4 on dually flapped substrates and find that in contrast to FEN1/Rad27, Mus81-Mms4 activity is impaired on such substrates, resulting in cleavage products that do not allow direct religation. We conclude that Mus81-Mms4, unlike FEN1/Rad27, does not prefer dually flapped substrates and is unlikely to function as a 3-flapase counterpart to the 5-flapase activity of FEN1/Rad27. We further find that joint molecule incision by Mus81-Mms4 occurs in a fashion determined by the branch point, regardless of the position of an upstream duplex end. These findings underscore the significance of a nick adjacent to a branch point for Mus81-Mms4 incision.
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