ORGANIZATION OF THE GENETIC-LOCUS FOR CHICKEN MYOSIN LIGHT-CHAIN KINASE IS COMPLEX - MULTIPLE PROTEINS ARE ENCODED AND EXHIBIT DIFFERENTIALEXPRESSION AND LOCALIZATION

We report that the generic locus that encodes vertebrate smooth muscle and nonmuscle myosin light chain kinase (MLCK) and kinase-related pro tein (KRP) has a complex arrangement and a complex pattern of expressi on. Three proteins are encoded by 31 exons that have only one variatio n, that of the first exon of KRP, and the genomic locus spans approxim ately 100 kb of DNA. The three proteins can differ in their relative a bundance and localization among tissues and with development. MLCK is a calmodulin (CaM) regulated protein kinase that phosphorylates the li ght chain of myosin II. The chicken has two MLCK isoforms encoded by t he MLCK/KRP locus. KRP does not bind CaM and is not a protein kinase. However, KRP binds to and regulates the structure of myosin II. Thus, KRP and MLCK have the same subcellular target, the myosin II molecular motor system. We examined the tissue and cellular localization of KRP and MLCK in the chicken embryo and in adult chicken tissues. We repor t on the selective localization of KRP and MLCK among and within tissu es and on a differential distribution of the proteins between embryoni c and adult tissues. The results fill a void in our knowledge about th e organization of the MLCK/KRP genetic locus, which appears to be a la te evolving regulatory paradigm, and suggest an independent and comple x regulation of expression of the gene products from the MLCK/KRP gene tic locus that may, reflect a basic principle found in other eukaryoti c gene clusters that encode functionally linked proteins. J. Cell. Bio chem. 70:402-413, 1998. (C) 1998 Wiley-Liss, Inc.