Domain mapping of Escherichia coli RecQ de®nes the roles of conserved N- and C-terminal regions in the

RecQ DNA helicases function in DNA replication, recombination and repair. Although the precise cellular roles played by this family of enzymes remain elusive, the importance of RecQ proteins is clear; mutations in any of three human RecQ genes lead to genomic instability and cancer. In this report, proteolysis is used to de®ne a two-domain structure for Escherichia coli RecQ, revealing a large (~59 kDa) N-terminal and a small (~9 kDa) C-terminal domain. A short N-terminal segment (7 or 21 residues) is also shown to be sensitive to proteases. The effects of removing these regions of RecQ are tested in vitro. Removing 21 N-terminal residues from RecQ severely diminishes its DNA-dependent ATPase and helicase activities, but does not affect its ability to bind DNA in electrophoretic mobility shift assays. In contrast, removing the ~9 kDa C-terminal domain from RecQ results in a fragment with normal levels of ATPase and helicase activity, but that has lost the ability to stably associ-ate with DNA. These results establish the biochem-ical roles of an N-terminal sequence motif in RecQ catalytic function and for the C-terminal RecQ domain in stable DNA binding