Fig. 3. AKAP149 is as a B-type lamin-specifier of PP1. (A) AKAP149-IPs were incubated with phosphorylase a and either 1 µM trypsin, 50 µM KNSRVTFSED (`RVXF') peptide, 50 µM KNSRATASED (`RAXA') peptide, or 1 µM I-2. Phosphorylase phosphatase activity was evaluated as the release of ³²P measured by scintillation counting and expressed as a percentage (±s.d.) of activity after trypsinization in duplicate experiments. (B) AKAP149-IPs were incubated with immunoprecipitated B-type lamins phosphorylated in vitro with rat ßPKC and [³²P]ATP. B-type lamin phosphatase activity was measured as in (A) in duplicate experiments. 50 µM SSPKGVLFSS (`RVXF') or SSPKGALFSS (`RAXF') peptides were used.