BISC401 Lecture Notes - Lecture 13: Guanine Nucleotide Exchange Factor, Karyopherin, Nuclear Pore

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Reversible phosphorylation and direction of mrnp nuclear export. Sr protein phosphorylation and dephosphorylation directs mrnp export across the nuclear pore complex. Mechanism: step 1: phosphorylated (yeast) sr protein npl3 binds nascent pre-mrnas functions as an adapter protein that promotes mrnp exporter binding, step 2: when polyadenylation is completed . It stimulates glc7 nuclear phosphatase to dephosphorylate npl3. Gle2 adapter protein that brings mrnp to npc: step 4: (now in cytoplasm) cytoplasmic protein kinase sky1 phosphorylates. Nuclear transport receptors escort proteins containing nls into the nucleus. All proteins found in the nucleus-such as histones, transcription factors, and dna and. Rna polymerases are synthesized in the cytoplasm and imported into the nucleus through the npc. Such proteins contain a nls that directs their selective transport into the nucleus. Experiment: normal pyruvate kinase by itself stays in cytosol, when a chimeric pyruvate kinase containing the sv40 nls at its n-terminus was expressed in cells, it was localized to the nucleus.

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