AN INTERACTION BETWEEN A SPECIFIED SURFACE OF THE C-TERMINAL DOMAIN OF RECA PROTEIN AND DOUBLE-STRANDED DNA FOR HOMOLOGOUS PAIRING

RecA protein and its homologs catalyze homologous pairing of dsDNA and ssDNA, a critical reaction in homologous genetic recombination in var ious organisms from a virus, microbes to higher eukaryotes. in this re action, RecA protein forms a nucleoprotein filament on ssDNA, which in turn binds to naked dsDNA for homology search. We suggested that the C-terminal domain of RecA protein plays a role in capturing the dsDNA. Here, we isolated the C-terminal domain as a soluble form and determi ned the solution structure by NMR spectroscopy. The overall folding of the NMR structure agrees with that of the corresponding part of the r eported crystal structure, but a remarkable difference was found in a solvent-exposed region due to intermolecular contacts in the crystal. Then, we studied the interaction between the C-terminal domain and DNA , and found that significant chemical shift changes were induced in a specific region by titration with dsDNA. SsDNA induced a much smaller chemical shift perturbation. The difference of DNA concentrations to g ive the half-saturation of the chemical shift change showed a higher a ffinity of the C-terminal region toward dsDNA. Combined with our previ ous results, these provide direct evidence that the defined region in the C-terminal domain furnishes a binding surface for DNA. (C) 1997 Ac ademic Press Limited.