Isolation of a novel RNA-binding protein and its association with a large ribonucleoprotein particle present in the nucleoplasm of tobacco cells.

A cDNA encoding a protein with a consensus sequence-type RNA-binding domain (CS-RBD) has been isolated from a Nicotiana sylvestris cDNA library. The deduced protein (designated 'RZ-1') contains CS-RBD in its N-terminal half, arginine/aspartic acid repeats in its center and a glycine-rich-C-terminal region in which a zinc finger motif of the CCHC type is present. The corresponding gene appears to be expressed constitutively in all tobacco organs. Immunocytochemical assays revealed that RZ-1 is localized in the nucleoplasm of tobacco cultured cells. Glycerol gradient fractionation of tobacco nuclear lysates showed that RZ-1 is associated with a large ribonucleoprotein particle of around 60 S in size. Nucleic acid-binding assays indicated that RZ-1 binds preferentially to poly (G) and both the CS-RBD and glycine-rich region are necessary for its binding activity. A possible role of RZ-1 is discussed.