HisB

The hisB gene, found in the enterobacteria (such as "E. coli"), in "Campylobacter jejuni" and in "Xylella"/"Xanthomonas" encodes a protein involved in catalysis of two step in histidine biosynthesis (the sixth and eight step), namely the bifunctional Imidazoleglycerol-phosphate dehydratase/histidinol-phosphatase.
The former function (), found at the N-terminal, dehydrated -erythroimidazoleglycerolphosphate to imidazoleacetolphosphate, the latter function (), found at the C-terminal, dephosphorylates -histidinolphosphate producing histidinol.
The firth step is catalysed instead by histadinolphosphate aminotransferase (encoded by "hisC")
The peptide is 40.5kDa and associates to form a hexamer (unless truncated)
In E. coli hisB is found on the hisGDCBHAFI operon
The phosphatase activity possess a substrate ambiguity and overexpression of hisB can rescue phosphoserine phosphatase (serB) knockouts.
Reactions.
hisB-N
hisB-C
Non-fusion protein in other species.
HIS3 from "Saccharomyces cerevisiae" is not a fused IGP dehydratase and hisidinol phosphatase, but an IGPD only (homologous to hisB-N). Whereas HIS2 is the HP (analogous to hisB-C, called hisJ in some prokaryotes).