This is an SH3 (SRC homology domain 3) domain found in RecD helicases (EC 3.6.4.12) that belong to the bacterial Superfamily 1B (SF1B). This superfamily of helicases translocate in a 5'-3' direction and are required for a range of cellular activities across all domains of life [2]. Structural analysis indicate that the extension of the 5'-tail of the unwound DNA duplex induces a large conformational change in the RecD subunit, that is transferred through the RecC subunit to activate the nuclease domain of the RecB subunit. The process involves this SH3 domain that binds to a region of the RecB subunit. Studies of RecD in E. coli also revealed that the SH3 domain interacts with the ssDNA tail in a location different to that normally occupied by a peptide in canonical eukaryotic SH3 domains, thus retaining the potential to bind peptide at the same time as the ssDNA tail [3].

1: DNA binding to RecD: role of the 1B domain in SF1B helicase activity. Saikrishnan K, Griffiths SP, Cook N, Court R, Wigley DB; EMBO J. 2008;27:2222-2229. PMID:18668125

2: Mechanistic basis of 5'-3' translocation in SF1B helicases. Saikrishnan K, Powell B, Cook NJ, Webb MR, Wigley DB; Cell. 2009;137:849-859. PMID:19490894

3: Mechanism for nuclease regulation in RecBCD. Wilkinson M, Chaban Y, Wigley DB; Elife. 2016; [Epub ahead of print] PMID:27644322