CLONING, EXPRESSION ANALYSIS, AND FUNCTIONAL CHARACTERIZATION OF PKL12, A MEMBER OF A NEW SUBFAMILY OF SER/THR KINASES

Abstract We report the cloning of the full-length cDNA of a new murine protein kinase, mPKL12. The sequence reveals a 305-amino-acid protein that contains the characteristic subdomains of the kinase superfamily and particular homology indicating a ser/thr specificity. We have also identified its human homologue gene (94% identical) and the putative homologue proteins from Saccharomyces cerevisiae and Arabidoposis thaliana. These four sequences appear to form a new subfamily of protein kinases, close in size to the theoretical minimal catalytic domain, therefore suggesting that they could be the catalytic unit of a more complex holoenzyme. Using Escherichia coli -purified protein, we have demonstrated that the mPKL12 enzyme possesses an intrinsic kinase activity, capable of phosphorylating enolase and also of promoting autophosphorylation, with a ser/thr specificity. Tissue expression analysis of mPKL12 showed that it is ubiquitously expressed, although at very low levels. RT-PCR analysis of several cell lines also supports this view, therefore suggesting that PKL12 may play a role in a very general cellular function, probably related with the secretory pathway.