Microspherule Protein 1 (MCRS1)

MCRS1 contains potential nuclear localization signals in its N-terminal half and a leucine zipper region in its C-terminal half. Western blot analysis detected a major p78 doublet at about 78 kD and minor bands at about 62 and 55 kD. In vitro transcription-translation of p78 cDNA resulted in a 55-kD protein, suggesting that the bands at 78 kD represent highly modified proteins. Western blot analysis of synchronized HeLa cells detected p78 expression only in early S phase. It was not expressed in nondividing HeLa cells or human foreskin fibroblasts. Immunolocalization of p78 in HeLa cells detected the protein predominantly in nuclei. However, in Hep-2 liver carcinoma cells, p78 localized to both nuclei and cytoplasm, and in HSV-infected Hep-2 cells, it localized in a few dense nuclear bodies or at the nuclear membrane.