MOLECULAR-CLONING OF A NOVEL SERINE THREONINE KINASE, MRK, POSSIBLY INVOLVED IN CARDIAC DEVELOPMENT/

We have isolated a novel member of putative serine/threonine kinase fr om a rat heart cDNA library using polymerase chain reaction methods, T he novel kinase is transcribed as 2.6 kb mRNA encoding for a protein o f 629 amino acids with the long C-terminal non-catalytic portion, Amin o acids analysis revealed that the N-terminal catalytic domain is 87% identical to the male-germ cell associated kinase (MAK), a cdc2-relate d serine/threonine kinase found to promote meiosis during spermatogene sis, Therefore, we designated this novel kinase as the MAK-related kin ase (MRK), MRK protein, with a molecular weight of 66 kD, was shown to phosphorylate itself and the exogenous substrates, histone H1 and mye lin basic protein, In addition, phosphoamino acid analysis confirmed t he serine/threonine-specific protein kinase activity of MRK, Although MRK was ubiquitous in adult rat tissues, the expression of MRK protein in embryos was restricted primarily to embryonic myocardium during ea rly organogenesis, This finding suggests that MRK may be a participant in cardiac development.