The Use of Translocatable Genetic Elements to Construct a Fine-structure Map of the Klebsiella pneumoniae Nitrogen Fixation (nif) Gene Cluster

Abstract

The transposons Tn5, Tn7 and Tn10 and bacteriophage Mu were used to derive insertion mutations in the K. pneumoniae nif gene cluster. A large number of deletion mutants were derived by imprecise excision of insertion mutations and these deletions were used to construct a fine-structure map of the nif cluster. Comparison of this genetic map with a physical map of the nif cluster derived by Reidel et al. showed a very good correlation between genetic and physical mapping methods. A new complementation group, designated nifU, was identified and mapped between nifN and nifS. Polarity studies on the 14 nif cistrons now identified suggests that they are organized in at least 7 transcriptional units and that all the multicistronic units are transcribed in the same direction.