The nucleotide sequence of the nifM gene of Klebsiella pneumoniae and identification of a new nif gene: nifZ

Abstract

A 1.4-kb PstI-HpaI DNA fragment carrying the Klebsiella pneumoniae nifM gene has been sequenced; nifM has been shown to encode a 30.6-kDa polypeptide. Two other open-reading frames were identified upstream of nifM. The one immediately upstream of nifM encodes a 16.6-kDa polypeptide which has been identified by in vitro transcription/translation in an Escherichia coli 30000 .times. g supernatant system: we propose to designate this gene nifZ. The sequence of the second open reading frame is incomplete but it does not correspond to nifV, the gene previously thought to be immediately upstream of nifM, and may therefore identify another new nif gene. Both nifM and nifZ have functional nif promoters with the characteristic-24, -12 consensus sequence, we find no evidence for a nifM upstream activator sequence. The role of nifZ in nitrogenase biosynthesis is unknown but its identification calls into question previous assertions that only nifM and nifH are required for the synthesis of nitrogenase Fe protein.