A NUCLEAR-LOCALIZATION SIGNAL OF HUMAN ARYL-HYDROCARBON RECEPTOR NUCLEAR TRANSLOCATOR HYPOXIA-INDUCIBLE FACTOR 1-BETA IS A NOVEL BIPARTITE TYPE RECOGNIZED BY THE 2 COMPONENTS OF NUCLEAR PORE-TARGETING COMPLEX

Aryl hydrocarbon receptor nuclear translocator (ARNT) is a component o f the transcription factors, aryl hydrocarbon receptor (AhR) and hypox ia-inducible factor 1, which transactivate their target genes, such as CYP1A1 and erythropoietin, in response to xenobiotic aromatic hydroca rbons and to low O-2 concentration, respectively, Since ARNT was isola ted as a factor required for the nuclear translocation of AhR from the cytoplasm in response to xenobiotics, the subcellular localization of ARNT has been of great interest, In this investigation, we analyzed t he subcellular distribution of ARNT using transient expression of a fu sion gene with P-galactosidase and microinjection of recombinant prote ins containing various fragments of ARNT in the linker region of gluta thione S-transferase/green fluorescent protein, We found a clear nucle ar localization of ARNT in the absence of exogenous li,bands to AhR, a nd identified the nuclear localization signal (NLS) of amino acid resi dues 39-61, The characterized NLS consists of 23 amino acids, and can be classified as a novel variant of the bipartite type on the basis of having tyro separate regions responsible for efficient nuclear transl ocation activity, but considerable deviation of the sequence from the consensus of the classical bipartite type. NLSs. Like the well charact erized NLS of the SV40 T-antigen, this variant bipartite type of ARNT NLS was also mediated by the two components of nuclear pore targeting complex, PTAC58 and PTAC97, to target to the nuclear rim in an in vitr o nuclear transport assay.