Novel properties of the protein kinase CK2-site-regulated nuclear- localization sequence of the interferon-induced nuclear factor IFI 16.
Members of the interferon-induced class of nuclear factors possess a putative CcN motif, comparable with that within proteins such as the simian virus 40 large tumour antigen (T-ag), which confers phosphorylation-mediated regulation of nuclear-localization sequence (NLS)-dependent nuclear import. Here we examine the functionality of the interferon-induced factor 16 (IFI 16) CcN motif, demonstrating its ability to target a heterologous protein to the nucleus, and to be phosphorylated specifically by the CcN-motif-phosphorylating protein kinase CK2 (CK2). The IFI 16 NLS, however, has novel properties, conferring ATP-dependent nuclear import completely independent of cytosolic factors, as well as binding to nuclear components. The IFI 16 NLS is not recognized with high affinity by the NLS-binding importin heterodimer, and transport mediated by it is insensitive to non-hydrolysable GTP analogues. The IFI 16 NLS thus mediates nuclear import through a pathway completely distinct from that of conventional NLSs, such as that of T-ag, but intriguingly resembling that of the NLS of the HIV-1 transactivator protein Tat. Since the IFI 16 CK2 site enhances nuclear import through facilitating binding to nuclear components, this represents a novel mechanism by which the site regulates nuclear-protein import, and constitutes a difference between the IFI 16 and Tat NLSs that may be of importance in the immune response.
Briggs
L J
LJ
Nuclear Signalling Laboratory, Division for Biochemistry and Molecular Biology, John Curtin School of Medical Research, Australian National University, P.O. Box 334, Canberra City, A.C.T. 2601, Australia.
Johnstone
R W
RW
Elliot
R M
RM
Xiao
C Y
CY
Dawson
M
M
Trapani
J A
JA
Jans
D A
DA
D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D000255:Adenosine Triphosphate / Q000494:pharmacology; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001685:Biological Factors / Q000032:analysis / Q000494:pharmacology; D047390:Casein Kinase II; D002457:Cell Extracts / Q000494:pharmacology; D002463:Cell Membrane Permeability; D002467:Cell Nucleus / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D003600:Cytosol / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D019281:Dimerization; D004797:Enzyme-Linked Immunosorbent Assay; D015696:Gene Products, tat / Q000737:chemistry / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting; D028884:Karyopherins; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism; D010750:Phosphoproteins; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011506:Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D016415:Sequence Alignment; D014407:Tumor Cells, Cultured
D001685:Biological Factors; D002457:Cell Extracts; D015696:Gene Products, tat; C489664:Ifi16 protein, mouse; D028884:Karyopherins; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; D010750:Phosphoproteins; D011506:Proteins; D011993:Recombinant Fusion Proteins; C076700:IFI16 protein, human; D010768:Phosphoserine; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases