FIG. 6.

ERK2, but not p38 and JNK, mediates phosphorylation of serine 105. (A) In vitro kinase reaction with bacterially purified wild-type (Wt) full-length GATA4 or the S105A mutant GATA4 incubated with purified ERK2 in the presence of [³²P]ATP and subjected to SDS-polyacrylamide gel electrophoresis. Both proteins were also incubated with purified p38α (B) and JNK1 (C) protein to assess phosphorylation. MBP and recombinant c-Jun were used as positive controls in the kinase assays. The arrow shows the migration of the full-length GST-GATA4 fusion protein, although degradation products of faster migration were also visible.