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Updated: Aug 6, 2026

Heterokaryon Technique for Analysis of Cell Type-specific Localization
Published on: March 11, 2011
Identification of a novel nuclear localization signal in Sam68
T Ishidate1, S Yoshihara, Y Kawasaki
1Department of Oncogene Research, Institute for Microbial Diseases, Osaka University, Suita, Japan.
Abstract:
Sam68, a nuclear RNA binding protein, binds to Src and is phosphorylated at tyrosine residues in an M-phase specific manner. Here we identified a stretch of 24 amino acid residues in the COOH-terminal portion of Sam68 which function as a nuclear localization signal. This signal sequence bears no apparent homology to any other known nuclear localization sequence. However, this sequence was found to contain a motif, PPXXR (P, Pro; R, Arg), which is conserved in various RNA binding proteins including hnRNP proteins. Replacement of Arg in this motif with Ala abolished the nuclear accumulation of a GFP fusion protein, suggesting that this residue is important in translocating the protein to the nucleus.
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