Zn-ribbon_9 is a Zn-ribbon domain rich in aromatic and positively charged amino acid residues. This C-terminal Zn-ribbon domain consists of two beta-strands acting as a scaffold for the two Zn knuckles. Both pairs of cysteines making up the two Zn knuckles are situated at highly conserved sharp beta-turns, an arrangement that facilitates the tetrahedral coordination of the divalent Zn ion. The two Zn-knuckle cysteine motifs are separated by 20 residues, 9 of which form an alpha-helix (helix 4).Structural modelling suggests this domain may bind nucleic acids. The domain appears to bind flaA-mRNA, thus contributing to flagellum formation and motility.