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Journal of Virology, February 2000, p. 1892-1899, Vol. 74, No. 4
Department of Molecular Biology, The Lerner Research
Institute, The Cleveland Clinic Foundation, Cleveland, Ohio
44195,1 and Graduate Program in
Molecular Virology,2 Department of
Biochemistry, and Department of Physiology and
Biophysics,3 Case Western Reserve University,
Cleveland, Ohio 44106
Received 4 August 1999/Accepted 13 November 1999
For determining cellular functions of the interferon-inducible
human cytoplasmic protein P56, we undertook a Saccharomyces cerevisiae two-hybrid screen that identified Int6 as a
P56-interacting protein. That the interaction also occurs in human
cells was confirmed by coimmunoprecipitation and the observed
cytoplasmic displacement of nuclear Int6 upon coexpression of P56.
Because Int6 has been claimed to be both a cytoplasmic and a nuclear
protein, we investigated the structural basis of this discrepancy. By
mutational analyses, we showed that the Int6 protein contains a
bipartite nuclear localization signal and a nuclear export signal at
the far end of the amino terminus. The 20 amino-terminal residues of
Int6, when they were attached to a different nuclear protein, were
sufficient to translocate that protein to the cytoplasm. Within this
region, replacement of any of the three leucine residues with alanine
destroyed the function of the export signal. The specific domain of P56
that is required for its interaction with Int6 was mapped using the yeast two-hybrid assay and a mammalian coimmunoprecipitation assay. Both assays demonstrated that the C-terminal region of P56 containing three specific tetratricopeptide motifs is required for this
interaction. In contrast, removal of an internal domain of P56 enhanced
the interaction, as quantified by the two-hybrid assay.
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Characterization of the Interaction between the
Interferon-Induced Protein P56 and the Int6 Protein Encoded by a Locus
of Insertion of the Mouse Mammary Tumor Virus
*
Corresponding author. Mailing address: Department of
Molecular Biology, NC20, The Lerner Research Institute, The Cleveland Clinic Foundation, 9500 Euclid Ave., Cleveland, OH 44195. Phone: (216)
444-0636. Fax: (216) 444-0512. E-mail: seng{at}ccf.org.
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