ASGSB 1999 Annual Meeting Abstracts

INTERACTION OF PLANT CHIMERIC CALCIUM/CALMODULIN-DEPENDENT PROTEIN KINASE WITH A HOMOLOG OF EUKARYOTIC ELONGATION FACTOR-1. W. Wang and B.W. Poovaiah. Laboratory of Plant Molecular Biology and Physiology, Department of Horticulture, Washington State University, Pullman, WA

A chimeric Ca²⁺/calmodulin-dependent protein kinase (CCaMK) was previously cloned and characterized in this laboratory (Proc. Natl. Acad. Sci. USA 92: 4897-4901, 1995). The yeast two-hybrid system was used to isolate genes encoding CCaMK substrates/interacting proteins. One of the cDNA clones obtained from the screening (LlEF-11) has high similarity with the eukaryotic elongation factor-1 (EF-1). CCaMK phosphorylated only one site (Thr-257) of LlEF-11 in a Ca²⁺/CaM-dependent manner. Interestingly Thr-257 is located in the putative tRNA-binding region of LlEF-11. Unlike CCaMK, a Ca2+-dependent protein kinase (CRPK2) phosphorylated multiple sites of LlEF-11 in a Ca²⁺-dependent, but CaM-independent manner (J. Biol. Chem. 274: 12001-12008, 1999). The phosphorylation sites for CRPK2 are different from that of CCaMK. This suggests that the phosphorylation of EF-1 by these two kinases may have different functional significance. In vitro binding assays revealed that CCaMK binds to LlEF-11 in a Ca2+-independent manner. Dissociation of CCaMK from EF-1 by Ca²⁺ and subsequent phosphorylation by CCaMK in a Ca2+/CaM-dependent manner suggest that these interactions may play a role in regulating the biological functions of EF-1. A better understanding of the regulation and function of CCaMK should increase our knowledge of Ca2+/CaM-mediated signaling as well as its role in plant development. 

(Supported by NASA grant NAG-10-0061 and NSF grant MCB 96-30337.)

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