Nucleic Acids Research, 2001, Vol. 29, No. 7 1476-1483
© 2001 Oxford University Press
SfiI endonuclease activity is strongly influenced by the non-specific sequence in the middle of its recognition site
Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, Bristol BS8 1TD, UK
The SfiI endonuclease cleaves DNA at the sequence GGCCNNNN
NGGCC, where N is any base and
is the point of cleavage. Proteins that recognise discontinuous sequences in DNA can be affected by the unspecified sequence between the specified base pairs of the target site. To examine whether this applies to SfiI, a series of DNA duplexes were made with identical sequences apart from discrete variations in the 5 bp spacer. The rates at which SfiI cleaved each duplex were measured under steady-state conditions: the steady-state rates were determined by the DNA cleavage step in the reaction pathway. SfiI cleaved some of these substrates at faster rates than other substrates. For example, the change in spacer sequence from AACAA to AAACA caused a 70-fold increase in reaction rate. In general, the extrapolated values for kcat and Km were both higher on substrates with inflexible spacers than those with flexible structures. The dinucleotide at the site of cleavage was largely immaterial. SfiI activity is thus highly dependent on conformational variations in the spacer DNA.
* To whom correspondence should be addressed. Tel: +44 117 928 7429; Fax: +44 117 928 8274; Email: s.halford{at}bristol.ac.uk
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