In experiments where RNAi was less efficient, hardly any reduction in nuclear export could be observed. the cytoplasm. Nuclear pore complexes (NPCs) are protein channels residing in the NE, through which the active and highly specific transport of RNA and protein between the nucleus and the cytoplasm occurs, a process known as nucleocytoplasmic transport (24, 54, 65). The NPC is usually a modular and complex structure, displaying eightfold rotational symmetry (10, 50). It is composed of a series of concentric rings Src Inhibitor 1 at the plane of the NE, with 80- to 100-nm filaments extending into the nucleus, distally connected to form a basket structure, and 50-nm filaments extending into the cytoplasm (22, 30, 50, 53). Approximately 30 proteins, termed nucleoporins, constitute the vertebrate NPC and Src Inhibitor 1 contribute to many of its functions (10). Many nucleoporins form subcomplexes, and they collectively afford the structural integrity of the NPC and its assembly and disassembly during mitosis in higher eukaryotes, as well as playing a functional role in nucleocytoplasmic transport (60, 65). Immunoelectron microscopy (EM) studies using a variety of techniques and antibodies have revealed ultrastructural localizations of nucleoporins within the NPC (for example, see reference 63). These localizations can be used to explain how certain substructures of the NPC contribute to specific functions. Definitive localization of nucleoporins has been important for developing models to explain selective translocation through the NPC Src Inhibitor 1 (8, 51, 54). For example, members of a subset of nucleoporins made up of FG repeats are thought to generate a hydrophobic barrier at the NPC, permeable only to transport-competent macromolecules, which suggests that they are localized at accessible regions of the NPCs, lining the translocation route (51, 54). Three vertebrate nucleoporins are reported to localize exclusively to the cytoplasmic face of the NPC, Nup214/CAN, Nup88, and Nup358/RanBP2. Nup214 has been localized close to the midplane of Src Inhibitor 1 the NE, possibly as a component of the cytoplasmic ring (34, 64), and interacts with Nup88 to form a stable subcomplex (6, 20, 41). The mechanism for targeting this Nup88-Nup214 subcomplex to the NPC during nuclear assembly apparently requires both proteins, since depletion of Nup214 from mouse embryos caused mislocalization of Nup88 from the NPC, and the Nup214 conversation domain name of Nup88 expressed in BHK cells mislocalized Nup214 to the cytoplasm (6, 18, 20). Nup88 is present at an estimated 32 copies/NPC, compared to only 8 copies of Nup214 (10), and the ultrastructural localization of Nup88 at the NPC is currently unknown. Nup358/RanBP2 is usually localized to the cytoplasmic filaments of the NPC (64, 67, 69). Transmission electron microscopy (TEM) analysis of purified Nup358/RanBP2 revealed a 36-nm filamentous structure, and depletion of Nup358 from egg extracts caused assembly of NPCs lacking detectable cytoplasmic filaments, indicating Nup358 as a major, and possibly the only, nucleoporin constituent of these filaments (12, 64). No nucleoporin binding partners have been found for Nup358; therefore, the molecular association of the cytoplasmic filaments with the NPC is usually unknown. Nup88 and also Nup214 represent possible candidates, although in vitro-assembled Nup214-depleted NPCs did have cytoplasmic filaments (64). Soluble transport receptors are carriers that mediate the active transport of macromolecules through the NPC (23, 60). Biochemical studies have shown that for groups of transport substrates there is a specific transport receptor that utilizes a subset of nucleoporins to translocate the NPC (46). Many nucleoporins have been shown to bind certain transport receptors in vitro, providing primary indication of their roles Rabbit Polyclonal to TAF1 in specific transport pathways. However, the precise roles of these proteins in vivo largely remain to be decided, and in vertebrates only a few nucleoporins have been shown to play dominant roles in specific transportation pathways using model systems, such as for example in vitro nuclear set up Src Inhibitor 1 of egg components, the usage of antibodies, or overexpression in cultured cells and knockout mice (for instance, see referrals 5, 58, and 63). Nup214 offers been proven to connect to.
Related Stories
December 10, 2024
March 2, 2023