the human tap nuclear rna factor contains a novel transportin-dependent nuclear localization signal...
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The Human Tap Nuclear RNA Factor Contains a Novel Transportin-dependent Nuclear Localization Signal That Lacks Nuclear Ex
port Signal FunctionRay Truant, Yibin Kang, and Bryan R. Cullen
871602
Shishi’s seminar
2000,11,16
Background:
‧ At least two possible protein mediators of mRNA export exist: heterogeneous nuclear ribonucleoproteins (hnRNPs) and Tap protein.
‧ Definitions of importinαβ , importin β binding domain (IBB) , nuclear localization signal (NLS) , nuclear export signal (NES) , transportin (Trn) , hnRNP A1 and M9 .
‧ M9: NLS/NES Tap-N: NLS
Background:
‧ At least two possible protein mediators of mRNA export exist: heterogeneous nuclear ribonucleoproteins (hnRNPs) and Tap protein.
‧ Definitions of importinαβ , importin β binding domain (IBB) , nuclear localization signal (NLS) , nuclear export signal (NES) , transportin (Trn) , hnRNP A1 and M9 .
‧ M9: NLS/NES Tap-N: NLS
‧ Functional domain organization of
human Tap
Transportin is necessary and sufficient for Tap-N-NLS-dependent nuclear import.
‧Competitive nuclear import assays.
‧ Transportin is sufficient for Tap-N-NLS-dependent nuclear import.
Direct binding of the Tap-N-NLS by Trn
‧In vitro binding assays.
‧Nuclear uptake of the Tap-N-NLS is sequence-specific.
Functional comparison of M9 and Tap-N-NLS
‧ Heterokaryon fusion nuclear shuttling assay.
‧HeLa cell microinjection assays.
Three types of Trn-dependent protein NLS sequences.
‧M9: specific for Trn , NLS/NES .
‧Ribosomal proteins: can also be mediate by Impβ ,NLS , no homology to M9.
‧Tap: no homology to M9 , but specific for Trn , compete with M9 , but lacks NES .Trn nuclear import factor may have evolved a specialized role to the return of mRNA export factors to the nucleus.
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