BACILLUS-SUBTILIS-168 RECR PROTEIN-DNA COMPLEXES VISUALIZED AS LOOPEDSTRUCTURES

The Bacillus subtilis 168 RecR protein bound to duplex DNA in the pres ence of ATP and divalent cations (Mg2+ and Zn2+) was visualized by ele ctron microscopy as a nearly spherical particle. A RecR homomultimer i s frequently located at the intersection of two duplex DNA strands in an interwound DNA molecule, generating DNA loops of variable length. T wo individual DNA molecules bound to the same protein are seen at a ve ry low frequency, if at all. The association of RecR with the intersec tion of two duplex DNA strands is more often seen in supercoiled than with relaxed or linear DNA. The RecR protein displays a slight but sig nificant preference for negatively supercoiled over linear DNA. The mi nimum substrate size for RecR protein is about 150 bp in length. A pos sible mechanism for RecR function in DNA repair is discussed.