RecQ helicases: multiple structures for multiple functions?

Approximately 1% of the open reading frames in the human genome encode proteins that function as DNA or RNA helicases. These enzymes act in all aspects of nucleic acid metabolism where the complementary strands of DNA:DNA or DNA:RNA duplexes require to be transiently opened. However, they perform wider roles in nucleic acid metabolism due to their ability to couple the energy derived from hydrolysis of ATP to their unidirectional translocation along strands of DNARNA. In this way, helicases can displace proteins from DNARNA, drive the migration of DNA junctions (such as the Holliday junction recombination intermediate), or generate superhelical tension in nucleic acid duplexes. Here, we review a subgroup of DNA helicase enzymes, the RecQ family, that has attracted considerable interest in recent years due to their role not only in suppression of genome instability, but also in the avoidance of human disease. We focus particularly on the protein structural motifs and the multiple assembly states that characterize RecQ helicases and discuss novel biophysical techniques to study the different RecQ structures present in solution. We also speculate on the roles of the different domains and oligomeric forms in defining which DNA structures will represent substrates for RecQ helicase-mediated transactions.