Human Rad50/Mre11 is a flexible complex that can tether DNA ends

The human Rad50 protein, classified as a structural maintenance of chromoso mes (SMC) family member, is complexed with Mre11 (R/M) and has important fu nctions in at least two distinct double-strand break repair pathways. To fi nd out what the common function of R/M in these pathways might be, we inves tigated its architecture. Scanning force microscopy showed that the complex architecture is distinct from the described SMC family members. R/M consis ted of two highly flexible intramolecular coiled coils emanating from a cen tral globular DNA binding domain. DNA end-bound R/M oligomers could tether linear DNA molecules. These observations suggest that a unified role for R/ M in multiple aspects of DNA repair and chromosome metabolism is to provide a flexible, possibly dynamic, link between DNA ends.