Nucleic Acids Research, Vol 25, Issue 19 3832-3839, Copyright © 1997 by Oxford University Press
A Deufel, T Hermann, R Kahmann and G Muskhelishvili
Efficient DNA inversion catalysed by the invertase Gin requires the cis-
acting recombinational enhancer and the Escherichia coliFIS protein.
Binding of FIS bends the enhancer DNA and, on a negatively supercoiled DNA
inversion substrate, facilitates the formation of a synaptic complex with
specific topology. Previous studies have indicated that FIS-independent Gin
mutants can be isolated which have lost the topological constraints imposed
on the inversion reaction yet remain sensitive to the stimulatory effect of
FIS. Whether the effect of FIS is purely architectural, or whether in
addition direct protein contacts between Gin and FIS are required for
efficient catalysis has remained an unresolved question. Here we show that
FIS mutants impaired in DNA binding are capable of either positively or
negatively affecting the inversion reaction both in vivo and in vitro. We
further demonstrate that the mutant protein FIS K25E/V66A/M67T dramatically
enhances the cleavage of recombination sites by FIS-independent Gin in an
enhancer- independent manner. Our observations suggest that FIS plays a
dual role in the inversion reaction and stimulates both the assembly of the
synaptic complex as well as DNA strand cleavage.
ARTICLES
Stimulation of DNA inversion by FIS: evidence for enhancer-independent contacts with the Gin-gix complex
Institut fur Genetik und Mikrobiologie der Universitat Munchen, Maria- Ward-Strasse 1a, 80638 Munchen, Germany.
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