Nucleic Acids Research, Vol 27, Issue 21 4121-4127, Copyright © 1999 by Oxford University Press
GJ Sharples, LM Corbett and P McGlynn
The Rap protein of phage lambda is an endonuclease that nicks branched DNA
structures. It has been proposed that Rap can nick D-loops formed during
phage recombination to generate splice products without the need for the
formation of a 4-strand (Holliday) junction. The structure specificity of
Rap was investigated using a variety of branched DNA molecules made by
annealing partially complementary oligo-nucleotides. On Holliday junctions,
Rap endonuclease shows a requirement for magnesium or manganese ions, with
Mn(2+)supporting 5-fold more cleavage than Mg(2+). The location of
endonuclease incisions was determined on 3'-tailed D-loop, bubble, flayed
duplex, 5'-flap and Y junction DNA substrates. In all cases, Rap
preferentially cleaves at the branch point of these molecules. With a
flayed duplex, incisions are made in the duplex adjacent to the
single-strand arms. Comparison of binding and cleavage specificities
revealed that Rap is highly structure- specific and exhibits a clear
preference for 4- and 3-stranded DNA over Y and flayed duplex DNA. Almost
no binding or cleavage was detected with duplex, partial duplex and
single-stranded DNA. Thus Rap endonuclease shows a bias for structures that
resemble D-loop and Holliday junction recombination intermediates.
ARTICLES
DNA structure specificity of Rap endonuclease
Institute of Genetics, University of Nottingham, Queens Medical Centre, Nottingham NG7 2UH, UK. gary.sharples@nottingham.ac.uk
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