Organization and sequence of histidine biosynthesis genes hisH, -A, -F, and -IE in Thermoanaerobacter ethanolicus

Nucleotide sequence analysis of a 3.5-kb chromosomal fragment from the low G + C Gram-positive bacterium Thermoanaerobacter ethanolicus revealed a clu ster of five contiguous open reading frames (ORFs) designated hisH, hisA, h isF, hislE, and ORF5. The first four ORFs showed homology to genes of the h istidine biosynthesis pathway, and ORF5 encoded a product with no significa nt similarities to polypeptides presently known. The hisH ORF was partial ( truncated by cloning) and ORF5 was adjacent to xylF, which codes for a xylo se-binding periplasmic protein. The five genes encoded putative proteins of >104, 237, 254, 216, and 169 amino acids, respectively. Amino acid sequenc e comparison of the four his gene products indicated closely related homolo gs in prokaryotes, varying from low G + C Gram-positive bacteria to archaea . This is the first report of his anabolic genes in a thermophilic anaerobi c bacterium.