OXYGEN-CONTROLLED REGULATION OF THE FLAVOHEMOGLOBIN GENE IN BACILLUS-SUBTILIS

A gene, hmp, which encodes a ubiquitous protein homologous to hemoglob in was isolated among genes from Bacillus subtilis that are induced un der anaerobic conditions. The hmp protein belongs to the family of two domain flavohemoproteins, homologs of which have been isolated from v arious organisms such as Escherichia coli, Alcaligenes eutrophus, and Saccharomyces cerevisiae. These proteins consist of an amino-terminal hemoglobin domain and a carboxy-terminal redox active site domain with potential binding sites for NAD(P)H and flavin adenine dinucleotide. The expression of hmp is strongly induced upon oxygen limitation, and the induction is dependent on a two-component regulatory pair, ResD an d ResE, an anaerobic regulator, FNR, and respiratory nitrate reductase , NarGHJI. The requirement of FNR and NarGHJI for hmp expression is co mpletely bypassed by the addition of nitrite in the culture medium, in dicating that fnr is required for transcriptional activation of narGHI I which produces nitrite, leading to induction of hmp expression. In c ontrast, induction of hmp was still dependent on resDE in the presence of nitrite. A defect in hmp in B. subtilis has no significant effect on anaerobic growth.