THE ROLE OF URIDYLYLTRANSFERASE IN THE CONTROL OF KLEBSIELLA-PNEUMONIAE NIF GENE-REGULATION

The glnD gene in enteric bacteria encodes a uridylyltransferase/uridyl yl-removing enzyme which acts as the primary nitrogen sensor in the ni trogen regulation (Ntr) system. We have investigated the role of this enzyme in transcriptional regulation of nitrogen fixation genes in Kle bsiella pneumoniae by cloning glnD from this organism and constructing a null mutant by insertional inactivation of the chromosomal gene usi ng the Omega interposon. K. pneumoniae glnD encodes a 102.3 kDa polype ptide which is highly homologous to the predicted products of both Esc herichia coli glnD and Azotobacter vinelandii nfrX. The glnD-Omega mut ant was unable to uridylylate P-II and was altered in adenylylation/de adenylylation of glutamine synthetase. Uridylyltransferase was require d for derepression of ntr-regulated promoters such as glnAp2 and pnifL but was not involved in the nif-specific response to changes in nitro gen status mediated by the nifL product. We conclude that a separate, as yet uncharacterised, nitrogen control system may be responsible for nitrogen sensing by NifL.