This clade of sequences is highly similar to the HisF protein, but generally represents the second HisF homolog in the genome where the other is an authentic HisF observed in the context of a complete histidine biosynthesis operon. The similarity between these WbuZ sequences and true HisFs is such that often the closest match by BLAST of a WbuZ is a HisF. Only by making a multiple sequence alignment is the homology relationship among the WbuZ sequences made apparent. WbuZ genes are invariably observed in the presence of a homolog of the HisH protein (designated WbuY) and a proposed N-acetyl sugar amidotransferase designated in WbuX in E. coli, IfnA in P. aeriginosa and PseA in C. jejuni. Similarly, this trio of genes is invariably found in the context of saccharide biosynthesis loci. It has been shown that the WbuYZ homologs are not essential components of the activity expressed by WbuX, leading to the proposal that these to proteins provide ammonium ions to the amidotransferase when these are in low concentration. WbuY (like HisH) is proposed to act as a glutaminase to release ammonium. In histidine biosynthesis this is also dispensible in the presence of exogenous ammonium ion. HisH and HisF form a complex such that the ammonium ion is passed directly to HisF where it is used in an amidation reaction causing a subsequent cleavage and cyclization. In the case of WbuYZ, the ammonium ion would be passed from WbuY to WbuZ. WbuZ, being non-essential and so similar to HisF that a sugar substrate is unlikely, would function instead as a amoonium channel to the WbuX protein which does the enzymatic work.