Identification and Initial Characterization of mSLK, a Murine Member of the Ste20 Family of Kinases

Protein kinases play a major role in the regulation of cellular growth. We isolated a murine cDNA encoding a novel serine/threonine kinase (referred to as mSLK) ubiquituously expressed during all stages of murine development and in all adult tissues examined. The cDNA codes for a 1233-amino-acid polypeptide characterized by an N-terminal catalytic domain and a large C-terminal region of unknown function. The sequence of the catalytic domain places mSLK in the STE20 family of cytoplasmic kinases. The noncatalytic domain does not show significant homology to any known protein. mSLK expressed in either COS7 cells or in bacteria was shown to contain kinase activity. The N-terminal fragment of mSLK was able to autophosphorylate on serine and threonine residues, phosphorylate threonine residues on a C-terminal fragment of the molecule, and phosphorylate exogenous substrates myelin basic protein and histone IIIin vitro.Furthermore, autophosphorylation of the catalytic domain was enhanced in the presence of the C-terminal fragment, which suggests a possible regulatory role for the C-terminal region of mSLK. A genomic clone of mSLK was isolated and used for fluorescencein situhybridization locating the mSLK gene on band D2 of mouse chromosome 19.