FIG. 6.

MafA phosphorylation is required to activate QR1 expression in NR cells. (A) MafA is phosphorylated in NR cells. Quail embryo NR cells were transfected with an RCAS-derived vector encoding WT MafA and metabolically labeled with [³³P]orthophosphate. Cellular lysates were immunoprecipitated with either preimmune (P) or MafA-directed (I) serum and subjected to Western blotting and autoradiography. (B) Chicken embryo NR cells were transfected with RCAS-derived vectors encoding WT or S14A/S65A MafA. Cell extracts were analyzed by direct Western blotting with MafA-directed serum. (C) Integrity of serines 14 and 65 is required for activation of QR1 expression by MafA. Chicken embryo NR cells were transfected with empty RCAS (RCAS), RCAS-MafA (WT), or RCAS-S14A/S65A (S14A/S65A), and cellular lysates were analyzed by direct Western blotting with anti-QR1 serum (upper panel) and with anti-β-actin antibody as a loading control (lower panel).