NUCLEOSIDE-DIPHOSPHATE KINASE-MEDIATED SIGNAL-TRANSDUCTION VIA HISTIDYL-ASPARTYL PHOSPHORELAY SYSTEMS IN ESCHERICHIA-COLI

Nucleoside-diphosphate kinase (NDP kinase), a key enzyme in nucleotide metabolism, is also known to be involved in growth and developmental control and tumor metastasis suppression. Interestingly, we find that coexpression of NDP kinase with Taz1, a Tar/EnvZ chimera, in the absen ce of its native signal, can activate a porin gene ompC-lacZ expressio n in Escherichia coli. Further studies show that NDP kinase can act as a protein kinase to phosphorylate histidine protein kinases such as E nvZ and CheA which are members of the His-Asp phosphorelay signal tran sduction systems in E. coli. Instead of ATP, the exclusive phosphodono r for histidine kinases, GTP can be utilized in vitro in the presence of NDP kinase to phosphorylate EnvZ and CheA, which then transfer the phosphoryl group to OmpR and CheY, the respective response regulators. The direct involvement of GTP for the phosphorylation of EnvZ through NDP kinase was further demonstrated by the use of a mutant EnvZ, whic h lost ability to be autophosphorylated with ATP. Phospho OmpR thus fo rmed can bind specifically to an ompP promoter sequence. These results suggest that NDP kinase may play a physiological role in signal trans duction.