BIOCHEMICAL ANALYSIS OF CLONED RHIZOBIUM JAPONICUM DNA CONTAINING THE NITROGENASE GENES

ABSTRACT The structural genes of the nitrogenase enzyme complex of Rhizobium japonicum were isolated from the total genome of this organism using recombinant DNA technology. A recombinant plasmid, pRJ676, was thus found in a clone bank. It contains a DNA region that has homology with the Klebsiella pneumoniae genes nifH and nifD, which code for two of the three polypeptides of the nitrogenase complex. The expression of several subfragments of pRJ676 was tested by cloning them into suitable vectors in such a way that they were transcribed from the strong promoters of antibiotic resistance genes. Transposon (Tn5) insertion mutations were used to determine the exact end points of transcriptional units. We postulate the existence of a transcriptional unit that is large enough to accomodate all three nitrogenase structural genes.