This is the N-terminal zinc finger domain present in reverse gyrase proteins. Most reverse gyrases conserve the N-terminal zinc finger of the zinc ribbon type, pointing to a crucial function of this domain. Structure of Thermotoga maritima reverse gyrase elucidates that the N-terminal zinc finger firmly attaches the H1 (helicase 1) domain to the topoisomerase domain contributing to double-strand DNA (dsDNA) binding [1].

1: Crystal structures of Thermotoga maritima reverse gyrase: inferences for the mechanism of positive DNA supercoiling. Rudolph MG, del Toro Duany Y, Jungblut SP, Ganguly A, Klostermeier D; Nucleic Acids Res. 2013;41:1058-1070. PMID:23209025