NUCLEOLIN INTERACTS WITH SEVERAL RIBOSOMAL-PROTEINS THROUGH ITS RGG DOMAIN

Nucleolin is one of the major nonribosomal proteins of the nucleolus, Through its four RNA-binding domains, nucleolin interacts specifically with pre-rRNA as soon as synthesis begins, but it is not found in mat ure cyto-plasmic ribosomes, Nucleolin is able to shuttle between the c ytoplasm and the nucleus. These data suggest that nucleolin might be i nvolved in the nucleolar import of cytoplasmic components and in the a ssembly of pre-ribosomal particles. Here we show, using two-dimensiona l blots in a ligand blotting assay, th at nucleolin interacts with 18 ribosomal proteins from rat (14 and 4 from the large and small subunit , respectively). The C-terminal domain of nucleolin (p50) interacts wi th 10 of these identified ribosomal proteins, In vitro binding assays show that the glycine-arginine rich, domain of nucleolin (RGG domain) is sufficient for the interaction with one of these proteins. Interest ingly, most of the proteins that interact with p50 belong to the core ribosomal proteins, which are resistant to extraction with high salt c oncentration. These findings suggest that nucleolin might be involved in the nucleolar targeting of some ribosomal proteins and in their ass embly within pre-ribosomal particles.