FUNCTIONAL DOMAINS OF NUCLEOLAR PHOSPHOPROTEIN P120

Nucleolar phosphoprotein p120 is a low abundance, proliferation-associ ated protein. Several functional domains have been characterized and a re discussed here such as the antigenic domain recognized by a monoclo nal antibody, the nuclear/nucleolar localization domain, phosphorylati on domains of casein kinase II (CKII) and protein kinase C, a putative methylation domain and an RNA binding region. By sucrose gradient sed imentation analyses, protein p120 was shown to rapidly sediment with 6 0-80 S pre-rRNP particles but sedimented more slowly when treated with RNAse or salt suggesting binding to RNA. Nucleolar protein p 120 diff ered from other nucleolar proteins such as C23 (nucleolin) and B23 (nu cleophosmin) which sedimented more slowly near the top of the gradient .