Cloning and expression of a cDNA encoding a novel protein serine/threonine kinase predominantly expressed in hematopoietic cells.

We have isolated a cDNA clone of a new member of protein serine/threonine kinases, MPK38, from a cDNA library constructed from the murine teratocarcinoma PCC4 cell line by the polymerase chain reaction. MPK38 was transcribed as an approx. 2.5 kb mRNA encoding for a protein of 643 amino acids. N-terminus of MPK38 contains the kinase catalytic domain which exhibits approximately 60% protein sequence identity with the SNF1 serine/threonine kinase family. The MPK38 cDNA directs the in vitro translation of two protein species of approx. 70 and approx. 50 kDa, which appear to result from an internal initiation of translation. MPK38 was predominantly expressed in thymus and spleen, but was not detectable in kidney, liver, and muscle in the adult tissues. In addition, MPK38 was apparently expressed in T lineage cells and a macrophage/monocyte cell, but was not detectable in a B cell line and an embryonic cell line. However, a low level of MPK38 transcript was detectable in a mast cell line after a longer exposure. Furthermore, MPK38 gene product showed the kinase activity which was assessed by immune complex kinase assay. Thus, MPK38 gene product seems to play an important role in signal transduction of certain lineages of hematopoietic cells.