REGULATION OF RECOMBINANT MEK1 AND MEK2B EXPRESSED IN ESCHERICHIA-COLI

Mitogen-activated protein kinase (MAPK) activation is an important sig nal involved in regulating cellular proliferation and/or differentiati on. The immediate upstream kinase MAPK kinase, referred to as MEK, act ivates MAPK by phosphorylation on specific tyrosine and threonine resi dues. To date, two MEK's have been cloned and characterized, MEK1 and MEK2. Here we report the cloning of MEK2b from mouse pituitary cDNA. R at and mouse MEK2 amino acid sequences vary by only three amino acids; the three changes are conserved in the MEK1 sequence. Analysis of rec ombinant MEK2b and MEK1 demonstrated similar activation by upstream ki nases and phosphotransferase activity toward MAPK, while they differed in autophosphorylation and the ability to serve as a substrate for MA PK. The findings demonstrate significant differences in potential regu latory mechanisms of MEK1 and MEK2/2b but not in their activation by u pstream regulators.