NOLP: Identification of a Novel Human Nucleolar Protein and Determination of Sequence Requirements for Its Nucleolar Localization

Abstract This study reports cDNA isolation and partial characterization of a novel human nucleolar protein isolated by “nuclear transportation trap” described previously. The cDNA encodes a putative polypeptide of 524 amino acids with a short Escherichia coli DNA helicase homologous region, an acid-rich domain, three potential base-rich nuclear localization signals (NLSs), a serine-rich domain, and a deduced coiled-coil domain. The protein has no known prominent similarities with any other protein in the protein databases. Tissue distribution analysis demonstrated a predominant expression in brain and testis. To determine the sequence requirements for nucleolar targeting, a set of deletion constructs with a fluorescent tag were transiently expressed in COS-7 cells. We revealed that a region of 30 amino acids (position 342–371), which overlaps the first and second NLS, is sufficient for nucleolar localization. Furthermore, the adjacent region of 30 amino acids (position 372–401), which contains the third NLS, is sufficient for nuclear localization. These results suggest that this novel nucleolar protein has at least two distinct domains for directing to different subnuclear destinations.