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J. Biochem, 2004, Vol. 135, No. 3 429-438
© 2004 The Japanese Biochemical Society

BIOCHEMISTRY

The Carboxyl-Terminus Directs TAFI48 to the Nucleus and Nucleolus and Associates with Multiple Nuclear Import Receptors

Joseph L. Dynes1, Shuping Xu*,2, Sarah Bothner3, Jill M. Lahti3 and Roderick T. Hori§,2

1 Reeve-Irvine Research Center, Department of Anatomy and Neurobiology, University of California, Irvine, CA 92697, USA; 2 Department of Molecular Sciences, University of Tennessee Health Science Center, 858 Madison Avenue, G01 Memphis, TN 38163, USA; and 3 Department of Tumor Cell Biology, St. Jude Children’s Research Hospital, Memphis, TN 38105, USA

The protein complex Selectivity Factor 1, composed of TBP, TAFI48, TAFI63 and TAFI110, is required for rRNA transcription by RNA polymerase I in the nucleolus. The steps involved in targeting Selectivity Factor 1 will be dependent on the transport pathways that are used and the localization signals that direct this trafficking. In order to investigate these issues, we characterized human TAFI48, a subunit of Selectivity Factor 1. By domain analysis of TAFI48, the carboxyl-terminal 51 residues were found to be required for the localization of TAFI48, as well as sufficient to direct Green Fluorescent Protein to the nucleus and nucleolus. The carboxyl-terminus of TAFI48 also has the ability to associate with multiple members of the ß-karyopherin family of nuclear import receptors, including importin ß (karyopherin ß1), transportin (karyopherin ß2) and RanBP5 (karyopherin ß3), in a Ran-dependent manner. This property of interacting with multiple ß-karyopherins has been previously reported for the nuclear localization signals of some ribosomal proteins that are likewise directed to the nucleolus. This study identifies the first nuclear import sequence identified within the TBP-Associated Factor subunits of Selectivity Factor 1.

* Current affiliation: Department of Urology, University of Pittsburgh Medical Center, Pittsburgh, PA 15232, USA.

§ To whom correspondence should be addressed. Tel: +901-448-6576, Fax: +901-448-7360, E-mail: rhori{at}utmem.edu


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