HisN from C. glutamicum is often identified predominately in higher GC Gram-positive bacteria (BLASTP). Pretty much all taxonomical orders on the class Actinobacteria contain genera with HisN homologues, like the Actinomycetales, Corynebacteriales, using the important families Corynebacteriaceae and Mycobacteriaceae, Frankiales, Micrococcales and Streptomycetales (information not shown). Because of the higher sequence similarity to IMPase it truly is hard to decide around the basis from the sequence alone if a hisN homologue encodes a Hol-P phosphatase. 4 genes exhibiting high sequence homology to hisNCg are currently present within the genome of C. glutamicum. These genes are cg0911, cg2090 (suhB), cg2298 (impA), and cg0967 (cysQ), all encoding proteins with domains common of inositol monophosphatases (Mormann et al., 2006). Deletion of hisN was reported to result in histidine auxotrophy in C. glutamicum (Mormann et al., 2006). Contrary to this, Jung and colleagues (2009) reported the cloning and identification of all C. glutamicum his genes without the need of mentioning the hisN gene and evidence for the want of such a gene by performing complementation research with histidine auxotrophic E. coli mutants. This discrepancy can be explained by the E. coli mutants utilised in the study of Jung and colleagues (2009). The E. coli hisB463 mutant used had a deletion from the distal part of the hisB gene encoding the imidazoleglycerol-phosphate dehydratase activity, however the histidinol phosphate phosphatase activity is not impacted in this strain (Struhl and Davis, 1977). We observed a strongly impaired growth of a C. glutamicum DhisN mutant on minimal medium, but no comprehensive histidine auxotrophy, indicating the existence of a minimum of 1 extra gene encoding a protein with HisN activity (R.K. Kulis-Horn, unpubl. obs.). Most likely, certainly one of the 4 hisNCg homologues present in C. glutamicum is able to partially complement the hisN deletion. Histidinol dehydrogenase (HisD) The final two measures of histidine biosynthesis are catalysed by a single enzyme. L-Histidinol is initially oxidized by histidinol dehydrogenase to L-histidinal, which can be additional oxidized to L-histidine (Alifano et al., 1996). Both methods are2013 The Authors. Microbial Biotechnology published by John Wiley Sons Ltd and Society for Applied Microbiology, Microbial Biotechnology, 7, 5Histidine in C. glutamicumFig. 2. Structure in the 4 histidine operons in C. glutamicum. Canonical histidine biosynthesis genes are depicted in dark blue. Genes shown in light blue exhibit higher sequence similarity to hisN. Genes shown in white have no apparent function in histidine biosynthesis. Arrows indicate the positions of putative major and internal promoters. Presence of a SD sequence is marked with an asterisk. The ruler indicates the absolute position inside the genome (depending on the genome version by Kalinowski et al.Zilovertamab vedotin , 2003 RefSeq NC_006958.Medroxyprogesterone acetate 1).PMID:24406011 The genes orf1 and orf2 correspond to genes cg2302 and cg2301 in C. glutamicum ATCC 13032 respectively. The release of the comprehensive genome sequence of C. glutamicum (Kalinowski et al., 2003) revealed that the hisN, hisGE, and hisDCB-cg2302-cg2301-hisHA-impA-hisFI loci are each separated by a number of hundred kilobase pairs forming independent transcriptional units (Fig. two). A closer look is needed to verify the operon structure of the hisDCB-cg2302-cg2301-hisHA-impA-hisFI locus. The conclusion that the genes hisDCB-orf1-orf2-hisHA-impAhisFI type one transcriptional unit in C. glutamicum AS019 is determined by outcome.