DNA endbinding speci®city of human Rad50/Mre11 is in¯uenced by ATP

The Rad50, Mre11 and Nbs1 complex is involved in many essential chromosomal organization pro-cesses dealing with DNA ends, including two major pathways of DNA double-strand break repair, hom-ologous recombination and non-homologous end joining. Previous data on the structure of the human Rad50 and Mre11 (R/M) complex suggest that a com-mon role for the protein complex in these processes is to provide a physical link between DNA ends such that they can be processed in an organized and coordinated manner. Here we describe the DNA binding properties of the R/M complex. The complex bound to both single-stranded and double-stranded DNA. Scanning force microscopy analysis of DNA binding by R/M showed the requirement for an end to form oligomeric R/M complexes, which could then migrate or transfer away from the end. The R/M complex had a lower preference for DNA substrates with 3¢-overhangs compared with blunt ends or 5¢-overhangs. Interestingly, ATP binding, but not hydrolysis, increased the preference of R/M binding to DNA substrates with 3¢-overhangs relative to substrates with blunt ends and 5¢-overhangs