Tuesday, May 15, 2012

SOMETHING UNUSUAL: RecA of Dinococcus radiodurans binds to double standed DNA first

The D. radiodurans RecA protein (361 amino acids, Mr 38,013) is 57% identical (72% similar) to the E. coli RecA protein (352 amino acids, Mr 37,842). In vitro, the protein promotes all of the key recombino genic activities of RecA-class recombinases. It forms filaments on DNA, hydrolyses ATP and dATP in a DNA-dependent fashion and promotes DNA-strand exchange. However, the D. radiodurans RecA protein has one distinct function. The DNA strand-exchange reactions of the E. coli RecA protein, and all other homologues examined to date, are ordered so that the single-stranded DNA is generally bound first, before the double-stranded DNA is bound.
 This order of DNA binding makes sense from a biological standpoint, as the RecA protein must be targeted to single-strand gaps at stalled replication forks and other damaged DNA sites. By contrast, the D. radiodurans RecA protein promotes an obligate inverse  DNA strand- exchange reaction, binding the duplex DNA first and the homologous single-stranded DNA substrate second. 

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