Cloning and characterization of a novel endoplasmic reticulum localized G-patch domain protein, IER3IP1.

The endoplasmic reticulum (ER) is the site of protein synthesis, folding, post-translational modifications and export. The ER membrane and its lumen contain various chaperones and enzymes that are involved in every aspect of the ER function. In this report, we identified a novel endoplasmic reticulum protein (immediate early response 3 interacting protein 1, IER3IP1) during the large-scale partial sequencing of a liver cDNA library. The full-length 1304 bp IER3IP1 cDNA has a predicted open reading frame (ORF), which encodes an 82 amino-acid protein possessing a G-patch domain. This domain is found in several RNA associated proteins and has been suggested to be involved in RNA binding. IER3IP1 gene was mapped to the chromosome 18q12 by radiation hybrid analysis. In northern blot hybridization, it was shown that IER3IP1 gene has a high expression in heart, skeletal muscle and kidney, a moderate expression in liver and brain and a low expression in placenta, lung and peripheral blood leukocyte. With the presence of transmembrane domain at the C-terminal, the translated IER3IP1 protein was localized to endoplasmic reticulum of HepG2 cells and was confirmed by co-localization with ER specific marker.