The ATP-dependent DNA helicase RecQ of E. coli is about 600 residues long. This model represents bacterial proteins with a high degree of similarity in domain architecture and in primary sequence to E. coli RecQ. The model excludes eukaryotic and archaeal proteins with RecQ-like regions, as well as more distantly related bacterial helicases related to RecQ. [DNA metabolism, DNA replication, recombination, and repair]