(A) Key residues for FRH function shown on the large-cell structure: K208 and S324 compose the ATP binding site, E294 lies between the ADP and RNA pockets and participates in ATP hydrolysis; P871 resides in the elbow region of the arch domain. K811, R806, R712 and K766 contribute to a positively charged surface on the KOW domain. R806H disrupts the clock. Q131, G132 and V142 in the N-terminus provide interactions to the helicase RecA domains (FRH domains are colored according to Fig1, ADP and RNA are in orange bonds). (B) Same as (A) after rotation about a horizontal axis. 