Importin β1 human

Importin β1 has 19 tandemly repeated HEAT (huntingtin, elongation factor 3 (EF3), protein phosphatase 2A (PP2A) and the yeast kinase TOR1) motifs. The gene is mapped to human chromosome 17q21. The protein shuttles between the cytoplasm and nucleus. It belongs to the importin β family of proteins.

Importin β, an import receptor, is a prototype of the nuclear transport receptor family, which comprises in human more than 20 proteins (90-180 kDa). These proteins interact directly with nuclear pore complex (NPC) and mediate nucleocytoplasmic transport. Importin β imports into the nucleus proteins carrying canonical nuclear localization signals (NLS) as well as UsnRNAs, which it binds via adaptor proteins, importin α and snurpotin-1 respectively. Importin β also binds directly, without adaptors, ribosomal proteins, Smad proteins, and virus derived proteins such as HIV Rev and Tat, that contain non classical NLS. In addition, Improtin b has been shown to be involved in the nuclear envelope assembly process.
The mechanism of importin β action in nuclear import can be demonstrated by the well-studied import of proteins containing classical NLS. Importin β forms a complex with Importin α, which, in turn, binds the cargo protein via its NLS. The Impβ/Impα/cargo complex translocates into the nucleus. When the complex reaches the nuclear site of the NPC, Ran-GTP binds the Impβ to form Impβ/Ran-GTP complex and released the Impα and the cargo protein. The Impβ/Ran-GTP complex is then exported to the cytoplasm where the complex dissociates upon hydrolysis of GTP to GDP, making Impβ ready for a new import cycle.

Solution in 5% glycerol containing 20 mM Hepes, pH 7.5, 110 mM potassium-acetate, 2 mM magnesium-acetate, 0.5 mM EGTA, 0.1 mM ATP, 2 mM DTT, and protease inhibitors.