PMS2 deficiency. (A) Mutations in the PMS2 gene. Mutations in PMS2 gene and predicted proteins. (B) PMS2 protein expression in patients' fibroblasts and EBV B cell lines by Western blot analysis. Antibody raised against the C terminus of PMS2 failed to detect PMS2 in P1 fibroblasts (n = 1), whereas an antibody raised against the N terminus revealed a truncated 46-kD protein (not found in control cells) in P1 fibroblasts (n = 3) and the EBV B cell line (n = 1). The antibody specific for the N terminus of PMS2 revealed no detectable protein in P2 EBV B cells (n = 3). MLH1 expression was found to be lower in P1 fibroblasts and in P1 and P2 EBV B cell lines (n = 3) compared with control cells. (C) Subcellular localization of PMS2. Primary fibroblasts from a control and P1 were labeled with anti–N-terminal PMS2 and anti-MLH1 antibodies, followed by secondary antibody (Alexa Fluor 488). PMS2 was predominantly observed in the cytoplasm in P1 fibroblasts, contrasting with a predominantly nuclear localization in control fibroblasts. No difference was observed in terms of the subcellular localization of MLH1, although MLH1 expression appeared to be slightly lower in P1 cells (n = 3). Bar, 20 μm.