Subcellular localization of interferon-inducible Myc/stat-interacting protein Nmi is regulated by a novel IFP 35 homologous domain.
Nmi was initially identified through a yeast two-hybrid interaction with N-Myc but it also interacts with c-Myc, Max, Fos, and several other transcription factors, including signal transducer and activator of transcription (Stat) proteins. Nmi is an interferon (IFN)-inducible protein with 25% amino acid identity to the IFN-inducible protein IFP 35. We have found that this homology consists of a novel domain of approximately 90-92 amino acids (aa) that is repeated in tandem in each protein. This region, termed Nmi/IFP 35 domain (NID), is important for subcellular localization of Nmi. Full-length Nmi protein or deletion constructs containing a single NID are localized to the cytoplasm, but amino-terminal Nmi fragments of up to 92 aa containing neither NID are nuclear. Fusion of the amino-terminal end of Nmi to pyruvate kinase, an exclusively cytoplasmic protein, results in a cytoplasmic fusion protein, suggesting that the amino-terminal end of Nmi does not contain a classic nuclear localization signal (NLS). Fusion of the amino-terminal end of Nmi to green fluorescent protein (GFP), which is normally found in both nuclear and cytoplasmic compartments, does not alter GFP distribution, whereas fusion of a single NID to GFP targets the fusion to the cytoplasm. Fusion of a nuclear localization signal (NLS) to full-length Nmi or NID repeats targets the hybrid to the nucleus, suggesting that a strong NLS is dominant to the cytoplasmic localization function of NID. NID may mediate cytoplasmic localization of the full-length Nmi protein through NID-NID protein interactions as demonstrated by yeast two-hybrid assay, immunoprecipitation, and the presence of Nmi in a high molecular weight protein complex. These results suggest that Nmi is composed of a modular structure with an amino-terminal domain that when separated from the rest of the protein is nuclear. The carboxy-terminal two thirds of the protein is composed of two NID that mediate cytoplasmic localization of the full-length protein.
Lee
N D
ND
Department of Pediatrics, Stanford Medical Center, CA 94305, USA.
Chen
J
J
Shpall
R L
RL
Naumovski
L
L
D000595:Amino Acid Sequence; D002352:Carrier Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D006801:Humans; D007369:Interferon Inducers / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D013347:Subcellular Fractions / Q000378:metabolism*
D002352:Carrier Proteins; D007369:Interferon Inducers; D047908:Intracellular Signaling Peptides and Proteins; C099927:NMI protein, human; D016271:Proto-Oncogene Proteins c-myc