Phosphorylation and peptide mapping of STEP isoforms from striatal slices treated with forskolin. A,Striatal slices prelabeled with [³²P]phosphate for 60 min were incubated with control buffer (lane 1) or forskolin (50 μm; lane 2) followed by immunoprecipitation of STEP isoforms, SDS-PAGE analysis, and autoradiography. The autoradiogram shows incorporation of [³²P]phosphate into STEP₆₁ and STEP₄₆. B, C, Gel pieces containing³²P-labeled STEP₆₁ (B) or STEP₄₆ (C) were excised and subjected to tryptic phosphopeptide mapping and autoradiography as described in Materials and Methods.