Functional expression in mammalian cells of a full‐length cDNA coding for the pp42/MAP kinase (p42mapk) protein

Abstract
We recently cloned from a mouse 3T3 cell cDNA library a cDNA with sequence similarity to the p42pmapk protein and other members of the MAP kinase family. To determine with certainty which member or the family this clone encodes, we have expressed the cDNA in COS cells and characterized the protein product. When the pSV2MAP plasmid carrying the full-length clone was transfected into COS cells, a protein of 42 000 Da was expressed. This 42 kDa protein displayed chromatographic properties indistinguishable from the endogenous p42mapk, and could be separated from the closely related pp44. In addition, upon serum stimulation, the 42 kDa protein became tyrosine-phosphorylated and enzymatically active towards the substrate myelin basic protein. We conclude that this clone codes for a functional p42mapk protein kinase