Kinetic study of the expression of Klebsiella pneumoniae nitrogen fixation ( nif) genes under conditions of inhibited transcription

Abstract

In vivo acetylene-reducing activity and the translation of nif mRNAs were examined in a N 2-fixing culture of Klebsiella pnuemoniae, following addition of NH 4 + ions, rifampicin, or both. The de novo biosynthesis of six [ 14C] pulse-labelled nif gene products was followed by gel electrophoresis (one and two dimensional). The amount of label incorporation into the nif-encoded polypeptides, which belong to four out of the seven nif transcriptional units, reflects the extent of translation of the corresponding mRNAs. A comparison of the results obtained under the three sets of conditions suggests : i) that the nif mRNAs examined appear to be more stable than the bulk cellular mRNAs ; ii) that the presence of NH 4 + ions does not affect the translation or most of the already pre-formed nif mRNAs.