In Haemophilus ducreyi, there is a frameshift sequence error between the HD1345 (encoding the N-terminal of NarQ) and HD1346 (encoding the C-terminal of NarQ). The combined the HD1345 and HD1346 are shown. Two possible missing fragments(underline) based on the proposed real starting codon in HD1345 and HD1346.

The cytoplasmic domains of NarQ contain three regions that are also conserved in the other bacterial two-component regulatory proteins and have been named the H, N, and G1 blocks. The H block contains a universally conserved histidine residue (e.g., NarQ His-378) that has been proposed to be the site of autophosphorylation on the basis of studies with other sensor-transmitter proteins. The NarQ proteins, along with three other proteins, UhpB, DegS, and ComP, form a distinct subfamily of bacterial sensor-transmitter pro-teins. A characteristic of this subfamily is the presence of a second conserved histidine (NarQ His-494) that is located four amino acids distant from an invariant asparagine residue (NarQ Asn-490) within the N block.