CHARACTERIZATION OF THE GLNK-AMTB OPERON OF AZOTOBACTER-VINELANDII

To determine whether in Azotobacter vinelandii the P-II protein influe nces the regulation of nif gene expression in response to fluxes in th e ammonium supply, the gene encoding P-II was isolated sand characteri zed. Its deduced translation product was highly similar to P-II protei ns from other organisms, with the greatest degree of relatedness being exhibited to the Escherichia coli glnK gene product. A gene designate d amtB was found downstream of and was cotranscribed with glnK as in E . coli. The AmtB protein is similar to functionally characterized ammo nium transport proteins from a few other eukaryotes and one other prok aryote, glnK and amtB comprise an operon. Attempts to isolate a stable glnK mutant strain were unsuccessful, suggesting that glnK, like glnA , is an essential gene in A. vinelandii. amtB mutants were isolated, a nd although growth on limiting amounts of ammonium was similar in the mutant and wild-type strains, the mutants were unable to transport [C- 14] methylammonium.