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Nucleoporin 50 Ran-binding domain NUP50 acts as a cofactor for the importin-alpha:importin-beta heterodimer, which allows for transportation of many nuclear-targeted proteins through nuclear pore complexes. It is thought to function primarily at the terminal stages of nuclear protein import to coordinate import complex disassembly and importin recycling. NUP50 is composed of a N-terminal NUP50 domain which binds the C-terminus of importin-beta, a central domain which binds importin-beta, and a C-terminal RanBD which binds importin-beta through Ran-GTP. NUP50:importin-alpha then binds cargo and can stimulate nuclear import. The N-terminal domain of NUP50 is also able to displace nuclear localization signals from importin-alpha. NUP50 interacts with cyclin-dependent kinase inhibitor 1B which binds to cyclin E-CDK2 or cyclin D-CDK4 complexes and prevents its activation, thereby controling the cell cycle progression at G1. Fungal Nup2 transiently associates with nuclear pore complexes (NPCs) and when artificially tethered to DNA, can prevent the spread of transcriptional activation or repression between flanking genes, a function termed boundary activity (BA). Nup2 and the Ran guanylyl-nucleotide exchange factor, Prp20, interact at specific chromatin regions and enable the NPC to play an active role in chromatin organization. Nup60p, the nup responsible for anchoring Nup2 and the Mlp proteins to the NPC is required for Nup2-dependent BA. Nup2 contains an N-terminal Nup50 family domain and a C-terminal RanBD. Ran is a Ras-like nuclear small GTPase, which regulates receptor-mediated transport between the nucleus and the cytoplasm. RanGTP hydrolysis is stimulated by RanGAP together with the Ran-binding domain containing acessory proteins RanBP1 and RanBP2. These accessory proteins stabilize the active GTP-bound form of Ran. RabBD shares structural similarity to the PH domain, but lacks detectable sequence similarity. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",