Structure of DNA-RecA protein complex, intermediate of homologous recombination, determined by polarised-light spectroscopy.

Abstract

The structure of long filament of DNA-RecA protein complex, active in homologous recombination, has been assessed using linear dichroism (LD) spectroscopy. The angular orientation of the DNA nucleobases relative to the fibre axis was estimated to be 70 degrees from the unique LD band of etheno-modified poly(dA) at 320 nm. Angular orientation data for 2 tryptophan and 7 tyrosine residues of RecA were deduced from differential LD of wild type RecA versus modified proteins which were engineered to attenuate the UV absorption of selected residues. The results revealed a rotation by some 40 degrees of the RecA subunits relative to the arrangement in crystal without DNA. Conformational changes are also indicated for tyrosine residues assigned to be involved in DNA binding or in RecA-RecA contacts.