This is the insert domain found in DNA gyrase B subunit proteins. Studies indicate that the insert has two functions, acting as a steric buttress to pre-configure the primary DNA-binding site, and serving as a relay that may help coordinate communication between different functional domains [1].

1: A domain insertion in Escherichia coli GyrB adopts a novel fold that plays a critical role in gyrase function. Schoeffler AJ, May AP, Berger JM; Nucleic Acids Res. 2010;38:7830-7844. PMID:20675723