Fig. 2. Sequence alignment of the helicase domains of the RecQ DNA helicases and the PcrA and Rep DNA helicases. The seven conserved helicase motifs, the point mutations of BLM protein as well as the insertion and deletions are displayed above the sequences, the ATP-binding (ÃÂ ) and DNA-binding residues (ÃÂ¤) of PcrA helicase are shown (24-26). Secondary structure elements of PcrA DNA helicase are indicated in red boxes for a helices and blue arrows for b strands. The symbols "~a~", "~b~", "~c~", and "~d~" represent the deletions of residues 117-194, 334-553 of PcrA, 109-185, 325-546 of Rep, respectively.