Nucleolar Protein 3 (NOL3)

Sequence analysis of the 219-amino acid NOP30 protein predicted that it contains a highly acidic N terminus and a basic C terminus enriched with arginines, serines, and prolines and having multiple phosphorylation sites. In contrast, SFRS9 is relatively strongly and ubiquitously expressed as a 1.35-kb transcript. In situ hybridization analysis showed that NOP30 is expressed in the pia mater, a tissue surrounding the brain containing blood vessels lined with smooth muscle cells. Binding analysis indicated that NOP30 binds to itself and that the N and C termini of NOP30 interact with SFRS9 through its RS domain. Confocal microscopy demonstrated that NOP30, through its arginine-rich C terminus, colocalizes with B23 (NPM1) in the granular component of nucleoli; however, the majority of NOP30 was localized in the fibrillar component.