FIGURE 10.

Comparison of sequences of a PcrA helicase from B. stearothermophilus (BACST) and from S. aureus (STAAU). PcrA from BACST translocates 3′→5′ (10), whereas PcrA from STAAU exhibits bipolar character (51). The two structures are shown aligned in tube format with the bound ATP in licorice format. PcrA from BACST is colored red and blue, whereas PcrA from STAAU is colored light red and light blue. Blue and light blue represent regions with identical sequences, whereas red and light red represent regions of variant sequences. In the regions of variant sequences (red and light red), there are 12 residues that also belong to the coevolutionarily determined core regions shown in Fig. 7, seven of which are located in domains 1A and 2A; in particular, three residues reside on helicase motifs VI and III, as indicated by arrows. The two residues located on motif VI are suggested here to be a dominant factor differentiating the translocation polarities of the two PcrA helicases.