Springer Online Journal Archives 1860-2000
Abstract Homologous recombination occurs at higher than average frequency at and near hotspots. Hotspots are special nucleotide sequences recognized by proteins that promote, directly or indirectly, a rate limiting step of recombination. This review focuses on two well-studied examples, the Chi sites of the bacteriumEscherichia coli and the M26 site of the fission yeastSchizosaccharomyces pombe. Chi, 5′ G-C-T-G-G-T-G-G 3′, is recognized by the RecBCD enzyme, which nicks the DNA near Chi and produces a 3′-ended single-stranded DNA ‘tail’; this tail is a potent substrate for homologous pairing by RecA and single-stranded DNA binding proteins. M26, 5′ A-T-G-A-C-G-T 3′, is recognized by a heterodimeric protein and stimulates, by an as-yet-unknown mechanism, meiotic recombination at and near theade6 gene. Additional hotspots in bacteria, fungi, and mammals enhance recombination directly or indirectly via a variety of mechanisms. Although hotspots are widespread among organisms, the biological role of their localized enhancement of recombination remains a matter of speculation.
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