CHARACTERIZATION OF BACILLUS-SUBTILIS HEMN

A recently cloned Bacillus subtilis open reading frame (hemN) upstream of the dnaK operon was identified as encoding a protein involved in o xygen-independent coproporphyrinogen III decarboxylation. B. subtilis hemN functionally complemented two Salmonella typhimurium hemF hemN do uble mutants under aerobic and anaerobic conditions. A B. subtilis hem N mutant accumulated coproporphyrinogen III only under anaerobic condi tions. Interestingly, growth experiments using the B. subtilis hemN mu tant revealed normal aerobic and anaerobic growth, indicating the pres ence of an alternative oxygen-independent enzymatic system. Northern b lot experiments identified hemN mRNA as part of an approximately 7-kb pentacistronic transcript consisting of lepA, hemN, hrcA, grpE, and dn aK. One potential start site for aerobic and anaerobic transcription w as located 37 bp upstream of the translational start codon of lepA. Co mparable amounts of hemN transcript were observed under aerobic and an aerobic growth conditions. No experimental evidence for the presence o f hemF in B. subtilis was obtained. Moreover, B. subtilis hemY did not substitute for hemF hemN deficiency in S. typhimurium. These results indicate the absence of hemF and suggest the presence of a second hemN -like gene in B. subtilis.