(A) Comparison of the FRH N-terminus (large cell structure, magenta) to that of Mtr4 (green) aligned on their RecA domains. Only the additional elements of FRH are shown (cyan). The FRH N-terminal extension has little ordered secondary structure, although regions 143-147 and 129-135 form small turns that interact with the helicase core. (B) The very N-terminus of FRH extends away from the RecA-2 domain to interact with a symmetry related molecule in the crystal (below), whereas the Mtr4 N-terminus turns back to form an outer β−strand. Center panel shows the crystal contacts, with close-ups for each region highlighted as insets on the left and right. 