IDENTIFICATION OF A NOVEL NUCLEAR-LOCALIZATION SIGNAL IN SAM68

Sam68, a nuclear RNA binding protein, binds to Src and is phosphorylat ed at tyrosine residues in an M-phase specific manner, Here we identif ied a stretch of 24 amino acid residues in the COOH-terminal portion o f Sam68 which function as a nuclear localization signal, This signal s equence bears no apparent homology to any other known nuclear localiza tion sequence, However, this sequence was found to contain a motif, PP XXR (P, Pro; R, Arg), which is conserved in various RNA binding protei ns including hnRNP proteins, Replacement of Arg in this motif with Ala abolished the nuclear accumulation of a GFP fusion protein, suggestin g that this residue is important in translocating the protein to the n ucleus. (C) 1997 Federation of European Biochemical Societies.