Genetic and biochemical analysis of mutants induced by bacteriophage Mu DNA integration into Klebsiella pneumoniae nitrogen fixation genes

Abstract

Polar mutations were obtained by integration of bacteriophage Mu c⁺ or Mu cts DNA into the Klebsiella pneumoniae nif genes located on plasmid pCE1, a derivative of pRD1. In addition, nif deletions were isolated from nif:: Mu cts plasmids. Complementation data allowed the characterization of twelve nif cistrons, nine corresponding to previously identified genes. Polar effect of Mu DNA insertions suggested the existence of at least six transcription units: 1) nifK, nifD and nifH-2) nifA and nifL-3) nifE and a new gene-4) nifB-5) nifF-6) nifJ. NifK, nifD and nifH, which are most probably the structural genes for nitrogenase, seem to belong to the same operon transcribed from nifH to nifK. This was confirmed by SDS gel autoradiography of pulse labelled proteins. Moreover it was possible to identify, on the autoradiograms, a polypeptide which likely is the product of nifJ and whose biosynthesis is under the control of nifA.