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キーワード:
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要旨:
RNA polymerase (Pol) II transcribes protein-coding
genes in the nucleus of eukaryotic cells and consists
of 12 polypeptide subunits. It is unknown how Pol II is
imported into the nucleus. Here we show that Pol II
nuclear import requires the protein Iwr1 and provide
evidence for cyclic Iwr1 function. Iwr1 binds Pol II in
the active center cleft between the two largest
subunits, maybe facilitating or sensing complete
Pol II assembly in the cytoplasm. Iwr1 then uses an
N-terminal bipartite nuclear localization signal that
is recognized by karyopherin a to direct Pol II nuclear
import. In the nucleus, Iwr1 is displaced from Pol II by
transcription initiation factors and nucleic acids,
enabling its export and recycling. Iwr1 function is
Pol II specific, transcription independent, and apparently
conserved from yeast to human.
