MOLECULAR-CLONING AND BIOCHEMICAL-CHARACTERIZATION OF A RECEPTOR-LIKESERINE THREONINE KINASE FROM RICE/

A receptor-like protein kinase, OsPK10, has been cloned from rice (Ory za sativa). The 2.8 kb cDNA contains an open reading frame capable of encoding a peptide sequence of 824 amino acids. The topological featur es of the predicted OsPK10 protein include an N-terminal signal peptid e, a cysteine-rich extracellular ligand-binding domain, a membrane-spa nning segment, and a cytoplasmic domain possessing all the hallmarks o f catalytic domains of eukaryotic protein kinases. The cytoplasmic dom ain was selectively expressed in Escherichia coli and assayed for kina se activity. The results show the protein is capable of autophosphoryl ation using either ATP or GTP as the phosphate donor. Phosphoamino aci d analysis reveals phosphorylation of threonines, consistent with the substrate specificity indicated by sequence motifs in the catalytic co re. A single amino acid substitution of Glu for Lys-528 completely abo lishes autophosphorylation activity. DNA gel blot analyses suggest tha t the haploid rice genome contains a single copy of the OsPK10 gene. O sPK10 transcripts appear to be more abundant in shoots than in roots o f rice seedlings.