BINDING OF Y-BOX PROTEINS TO RNA - INVOLVEMENT OF DIFFERENT PROTEIN DOMAINS

Eukaryotic Y-box proteins are reported to interact with a wide variety of nucleic acid structures to act as transcription factors and mRNA m asking proteins. The modular structure of Y-box proteins includes a hi ghly conserved N-terminal cold-shock domain (CSD, equivalent to the ba cterial cold-shock proteins) plus four basic C-terminal domains contai ning arginine clusters and aromatic residues. In addition, the basic d omains are separated by acidic regions which contain several potential sites for serine/threonine phosphorylation. The interaction of Y-box proteins, isolated from Xenopus oocytes (FRGY2 type), with RNA molecul es has been studied by UV crosslinking and protein fragmentation. We h ave identified two distinct binding activities. The CSD interacts pref erentially with the polypurines poly(A,G) and poly(G) but not poly(A), this activity being sensitive to 5 mM MgCl2 but not to 5 mM spermidin e. In the presence of 1 mM MgCl2 or 1 mM spermidine, the basic domains interact preferentially with poly(C,U), this activity being sensitive to 0.5 M NaCl. Binding of the basic domains is also sensitive to low concentrations of heparin. The basic domains can be crosslinked indivi dually to labelled RNA. These results are discussed with reference to the various specificities noted in the binding of Y-box proteins to RN A and DNA.