CHARACTERIZATION OF THE GLNB GENE-PRODUCT OF NOSTOC PUNCTIFORME STRAIN ATCC-29133 - GLNB OR THE P-II PROTEIN MAY BE ESSENTIAL

Bacterial P-II proteins, encoded by glnB genes, are central signalling molecules in nitrogen regulatory pathways and are modulated by post-t ranslational modification in response to the cellular nitrogen status. The glnB gene was cloned from the filamentous heterocyst-forming cyan obacterium Nostoc punctiforme strain ATCC 29133 (PCC 73102) by heterol ogous hybridization to a Synechococcus sp. strain PCC 7942 gene fragme nt. Expression of the cloned gene was verified by hybridization to IV. punctiforme total RNA and a single cross-reactive polypeptide was obs erved in immunoblots of N. punctiforme extracts probed with anti-Synec hococcus 7942 P-II antiserum. Modification of the purified N. punctifo rme P-II protein by a Synechococcus 7942 P-II kinase was observed, but modified forms of P-II were not detected in extracts of N. punctiform e from a variety of incubation conditions. The N. punctiforme glnB gen e could not be disrupted by targeted gene replacement unless a second copy of glnB was provided in trans, suggesting that the gene or gene p roduct is essential for growth under the conditions tested.