Immunoprecipitation experiment. A, Schematic of experimental design for immunoprecipitation experiment. p38 was incubated with varying amounts of MK2 as described in Methods. Following reaction, total p38 was immunoprecipitated and then reacted with 100 nM ATF2. B, ATF2 phosphorylation, following the experimental design described in A, was measured for varying MK2 concentrations.