NUCLEOLAR PROTEIN P120 CONTAINS AN ARGININE-RICH DOMAIN THAT BINDS TORIBOSOMAL-RNA

Human proliferation-associated protein p120 has previously been shown to localize to the nucleolus, and several functional domains of p120 h ave been elucidated. By using a nitrocellulose filter binding assay an d a Northwestern blotting procedure this study shows that recombinant p120 binds to an rRNA fragment in vitro with a dissociation constant o f 4 nM. The specific RNA-binding region of p120 (residues 1-57) was id entified with glutathione S-transferase-fused p120 deletion constructs and Northwestern blotting procedures. This RNA-binding region of p120 , which includes the nucleolar localization signal of p120, is similar to the arginine-rich RNA-binding regions found in other RNA-binding p roteins such as HIV Rev and Tat. Experiments in viuo with HeLa cell nu cleolar extracts showed that p120 was associated with the 60-80 S pre- ribosomal particles. This association is disrupted by treatment with e ither RNase A or buffer of high ionic strength. These results suggest that p120 might be involved in rRNA/ribosome maturation, consistent wi th the role of the yeast homologue Nop2p in rRNA biogenesis.