Biochemistry Section, Laboratory of Retinal Cell and Molecular Biology, and the Immunology and Virology Section, National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892-2740, USA. krishnan@helix.nih.gov
We have characterized NORPEG, a novel gene from human retinal pigment epithelial cells (ARPE-19), in which its expression is induced by all-trans-retinoic acid. Two transcripts ( approximately 3 and approximately 5 kilobases in size) have been detected for this gene, which is localized to chromosome band 5p13.2-13.3. Placenta and testis showed the highest level of expression among various human tissues tested. Six ankyrin repeats and a long coiled-coil domain are present in the predicted sequence of the NORPEG protein, which contains 980 amino acid residues. This approximately 110-kDa protein was transiently expressed in COS-7 cells as a FLAG fusion protein and immunolocalized to the cytoplasm. Confocal microscopic analysis of the NORPEG protein in ARPE-19 cells showed threadlike projections in the cytoplasm reminiscent of the cytoskeleton. Consistent with this localization, the expressed NORPEG protein showed resistance to solubilization by Triton X-100 and KCl. An ortholog of NORPEG characterized from mouse encoded a protein that showed 91% sequence similarity to the human NORPEG protein. The expression of Norpeg mRNA was detected in mouse embryo at embryonic day 9.5 by in situ hybridization, and the expression appears to be developmentally regulated. In adult mouse, the highest level of expression was detected in the seminiferous tubules of testis.