<p>1-(5-phosphoribosyl)-5-[(5-phosphoribosylamino)methylideneamino] imidazole-4-carboxamide isomerase (<db_xref db="EC" dbkey="5.3.1.16"/>), also known as Phosphoribosylformimino-5-aminoimidazole carboxamide ribotide isomerase or HisA, catalyses the fourth step in histidine biosynthesis. HisA from <taxon tax_id="1358">Lactococcus lactis</taxon> was found to be inactive [<cite idref="PUB00008010"/>].The putative HisA from <taxon tax_id="2336">Thermotoga maritima</taxon>, is a conspicuous outlier to the set of all other HisA, including experimental HisA from the bacterium <taxon tax_id="562">Escherichia coli</taxon> and the Archaeaon <taxon tax_id=" 2188">Methanococcus voltae</taxon>. Neighbor joining shows HisA from <taxon tax_id="2336">Thermotoga maritima</taxon> to be within the HisA family (with HisF as an outgroup) but with a long branch. </p> Phosphoribosylformimino-5-aminoimidazole carboxamide ribotide isomerase HisA