IDENTIFICATION OF MAPKAPK HOMOLOG (MAPKAPK-4) AS A MYOSIN-II REGULATORY LIGHT-CHAIN KINASE IN SEA-URCHIN EGG EXTRACTS

We identified and cloned a homolog of mammalian mitogen-activated prot ein kinase-activated protein kinase (MAPKAPK)-2 and -3 from sea urchin , Hemicentrotus pulcherrimus. The obtained cDNA clone was composed of 350 amino acid residues which contain MAPK phosphorylation sites and t he bipartite nuclear localization signal sites in its C-terminal domai n, The clone showed 65.4 and 66.7% amino acid residue identity to huma n MAPKAPK-2 and -3, respectively, Phylogenetic analysis revealed that the homolog can be classified into a distinct group of MAPKAPK and, th erefore, the identified homolog was designated as MAPKAPK-4. Biochemic al characterization was performed using recombinant glutathione S-tran sferase (GST)-MAPKAPK-4 fusion protein, The protein kinase activity of GST-MAPKAPK-4 was activated by MAPK and this enabled the kinase to ph osphorylate both glycogen synthase N-terminal peptide and the regulato ry light chain of myosin II in vitro, Northern blot analysis showed th at MAPKAPK-4 was expressed throughout the development of sea urchin em bryos, These observations suggest that MAPKAPK-4 may play an important role in the regulation of myosin II activity during the development o f sea urchin. (C) 1997 Academic Press