MXI2, A MITOGEN-ACTIVATED PROTEIN-KINASE THAT RECOGNIZES AND PHOSPHORYLATES MAX PROTEIN

We describe Mxi2, a human protein that interacts with Max protein, the heterodimeric partner of the Myc oncoprotein. Mxi2 encodes a 297-resi due protein whose sequence indicates that it is related to extracellul ar signal-regulated kinases (ERK protein kinases). Mxi2 in yeast inter acts with Max and with the C terminus of c-Myc. Mxi2 phosphorylates Ma x both in vitro and in vivo. The Mxi2 putative substrate recognition r egion has sequence similarity to the helix-loop-helix region in Max an d c-Myc, suggesting that substrate recognition might be mediated via t his motif. Phosphorylation by Mxi2 may affect the ability of Max to ol igomerize with itself and its partners, bind DNA, or regulate gene exp ression.