This is a cys-rich region (CRR) domain found in PriA DNA helicases. In bacteria, the replication restart process is orchestrated by the PriA DNA helicase, which identifies replication forks via structure-specific DNA binding and interactions with fork-associated ssDNA-binding proteins (SSBs). The CRR region which is embedded within the C-terminal helicase lobe has been identified to bind two Zn2+ ions. This 50-residue insertion forms a structure on the surface of the helicase core in which two Zn2+ ions are coordinated by invariant Cys residues. Biochemical experiments have shown that sequence changes to Zn2+-binding Cys residues in the PriA CRR can eliminate helicase, but not ATPase, activity and can block assembly of PriB onto DNA-bound PriA, implicating the CRR in multiple functions in PriA [1].

1: Structural mechanisms of PriA-mediated DNA replication restart. Bhattacharyya B, George NP, Thurmes TM, Zhou R, Jani N, Wessel SR, Sandler SJ, Ha T, Keck JL; Proc Natl Acad Sci U S A. 2014;111:1373-1378. PMID:24379377