EXPRESSION OF 3 MEMBERS OF THE CALCIUM-DEPENDENT PROTEIN-KINASE GENE FAMILY IN ARABIDOPSIS-THALIANA

Calcium-dependent protein kinases (CDPKs) belong to a unique family of enzymes containing a single polypeptide chain with a kinase domain at the amino terminus and a putative calcium-binding EF hands structure at the carboxyl terminus. From Arabidopsis thaliana, we have cloned th ree distinct cDNA sequences encoding CDPKs, which were designated as a tcdpk6, ntcdpk9 and atcdpk19. The full-length cDNA sequences for atcdp k6, atcdpk9 and atcdpk19 encode proteins with a molecular weight of 59 343, 55376 and 59947, respectively. Recombinant at CDPK6 and at CDPK9 proteins were fully active as kinases whose activities were induced by Ca2+. Biochemical studies suggested the presence of an autoinhibitory domain in the junction between the kinase domain and the EF hands str ucture. Serial deletion of the four EF hands of at CDPK6 demonstrated that the integrity of the four EF hands was crucial to the Ca2+ respon se. All the three atcdpk genes were ubiquitously expressed in the plan t as demonstrated by RNA gel blot experiments. Comparison of the genom ic sequences suggested that the three cdpk genes have evolved differen tly. Using antibodies against at CDPK6 and at CDPK9 for immunohistoche mical experiments, CDPKs were found to be expressed in specific cell t ypes in a temporally and developmentally regulated manner.