SummaryThe phenotype of a recently‐described mutant (OVG), conditionally defective in chromosome partitioning and septal positioning, was originally thought to be due to a new gene (parD) mapping at 88.4 min. We have now shown that, in addition to theparDmutation, OV6 carries agyrAammutation and that this mutation is probably responsible for the gross phenotype of the mutant. We have cloned thegyrAgene, identified the GyrA protein, sequenced thegyrAgene and flanking genes, cloned and sequenced thegyrAam, mutation, and identified its truncated product, in addition, we have identified the transcriptional start point of thegyrAgene. TheE. coliGyrA protein has extensive homologies with Gyrase proteins of other organisms and weak sequence homologies with some eukaryotic cytoskeletal protein