Escherichia coli helicase II (UvrD) protein initiates DNA unwinding at nicks and blunt ends

G. T. Runyon, D. G. Bear, T. M. Lohman

Research output: Contribution to journalArticlepeer-review

94 Scopus citations

Abstract

The Escherichia coli uvrD gene product, helicase II, is required for both methyl-directed mismatch and uvrABC excision repair and is believed to function by unwinding duplex DNA. Initiation of unwinding may occur specifically at either a mismatch or a nick, although no direct evidence for this has previously been reported. It has recently been shown that helicase II can unwind fully duplex linear and nicked circular DNA with lengths of at least ~2700 base pairs in vitro; hence, a flanking region of single-stranded DNA is not required to initiate DNA unwinding. In studies with uniquely nicked duplex DNA, we present EM evidence that helicase II protein initiates DNA unwinding at the nick, with unwinding proceeding bidirectionally. We also show that helicase II protein initiates DNA unwinding at the blunt ends of linear DNA, rather than in internal regions. These data provide direct evidence that helicase II protein can initiate unwinding of duplex DNA at a nick, in the absence of auxiliary proteins. We propose that helicase II may initiate unwinding from a nick in a number of DNA repair processes.

Original languageEnglish
Pages (from-to)6383-6387
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume87
Issue number16
DOIs
StatePublished - 1990

Keywords

  • DNA repair
  • electron microscopy
  • helicase

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