FIG. 1.

ERK2-Δ19-25 mutants do not bind to MEK1. (A) Murine ERK2 was subcloned into the pCDNA3 expression vector in frame with a sequence coding for an N-terminal FLAG tag (16). The sequence of the N terminus from residues 16 to 30 is shown up to the first glycine in the kinase domain using the single-letter code for amino acids. Residues that were deleted are underlined, while substitution mutations to alanine are boxed. (B) COS-1 cells were cotransfected with HA-MEK1 and a FLAG-ERK2 mutant. The following day HA-MEK1 immunoprecipitates (IP) were prepared as described in Materials and Methods and were immunoblotted with anti-HA and anti-FLAG antibodies.