HOMOLOGOUS DNA PAIRING PROMOTED BY A 20-AMINO ACID PEPTIDE DERIVED FROM RECA

The molecular structure of the Escherichia coli RecA protein in the ab sence of DNA revealed two disordered or mobile loops that were propose d to be DNA binding sites. A short peptide spanning one of these loops was shown to carry out the key reaction mediated by the whole RecA pr otein: pairing (targeting) of a single-stranded DNA to its homologous site on a duplex DNA. In the course of the reaction the peptide bound to both substrate DNAs, unstacked the single-stranded DNA, and assumed a beta structure. These events probably recapitulate the underlying m olecular pathway or mechanism used by homologous recombination protein s.