110C Lec15 mRNA export and translational control

110C Lec15 mRNA export and translational control - Lecture...

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Unformatted text preview: Lecture 15 mRNA export and translational control Reading: Lodish chapters 8.3; pages 351-356 & 570-575 15-1 mRNA transport from the nucleus across the nuclear envelope and into the cytoplasm Full processed [spliced and polyadenylated (will be discussed in detail in lectures 22 & 23) mRNAs in the nucleus remain bound in complexes together with a heterogeneous group of nuclear proteins (hnRNP). These complexes sometimes referred to as nuclear mRNA, or mRNP. The nuclear envelope is a double membrane, each of which is made up of a phospholipid bilayer similar to that of the plasma membrane. mRNPs and other macromolecules such as tRNAs, ribosomal RNA subunits, cross the nuclear envelope through nuclear pores . The nuclear pore complexes (NPCs) controls import and export of macromolecules such as RNA and protein ( cargo ) from the nucleus to the cytoplasm ( nuclear trafficking ). 15-2 The nuclear pore complex (NPC) is one of the largest protein assemblies in the cell. The total molecular mass is 60-80 million Da. They are composed of multiple copies of ~30 proteins, called nucleoporins . The pores are octagonal, and have 8 filaments extending 100 nm into the nucleoplasm joined to a terminal ring forming the nuclear basket. The other ends of the filaments attach to the nuclear lamina, a lamin intermediate filament meshwork that extends over the cytoplasmic side of the inner nuclear membrane. 8 filaments extend into the cytoplasm. The nuclear pore complexes microdissected from the large nuclei of Xenopus oocytes visualized by field emission in-lens scanning electron microscopy. (Left) cytoplasmic face reveals the octagonal shape. (Right) nucleoplasmic view shows the nuclear basket extending from the membrane. Cutaway model of the pore complex. The nuclear pore Central transporter 15-3 Large molecules like protein and RNA must be transported through the nuclear pore. They are assisted through this barrier by a family of nuclear transporters, which have hydrophobic regions on their cell surface (dark blue dots in the cartoon). These regions are thought to bind reversibly to the FG-domains of the FG- nucleoporins. This allows these proteins to move through the FG- nucleoporin barrier in the center of the nuclear pore, and thus to enter or exit the nucleus. A class of nucleoporins called FG-nucleoporins line the central channel of the nuclear pore. FG- nucleoporins contain long stretches of hydrophilic amino acids punctuated with hydrophobic FG- repeats (dark blue dots), which are short sequences rich in hydrophobic phenylalanine (F) and glycine (G) residues. The FG-repeat domains of the FG-nucleoporins in the central channel of the NPC. The FG-repeat domains are thought to interact with each other rapidly and reversibly, forming a molecular sieve which allows the diffusion of small molecules through it. However, it prevents the passage of larger molecules....
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110C Lec15 mRNA export and translational control - Lecture...

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