Multiple phosphorylated isoforms of NRL are expressed in rod photoreceptors

NRL, a bZIP transcription factor of the Maf subfamily, interacts with the h omeodomain protein CRX and synergistically regulates rhodopsin expression. Here we report that six isoforms of NRL (29-35 kDa) are generated by phosph orylation and expressed specifically in the mammalian retina. The anti-NRL antibody also crossreacts with a cytosolic 45-kDa protein, which is detecte d in neuronal tissues but is not encoded by the NRL gene. In both human ret inal cell cultures and sections of fetal and adult human retina, NRL is pre sent in the nuclei of developing and mature rods but not cones. We propose that NRL regulates rod photoreceptor-specific gene expression and is involv ed in rod differentiation.