Question

A. Discuss how nuclear import receptors such as importin function to carry proteins into the nucleus. Discuss: 1) how nuclear import receptors choose proteins for import: 2) the mechanism by which they get into the nucleus, including any other structures, molecules or molecular interactions involved; and 3) the mechanism by which nuclear proteins are released into the nucleus, as well as any important molecular interactions that are necessary for this process

Answer 1

1. Ans- NLS mediated protein trafficking by measuring biomolecular dynamics within loving cells using two-photon fluorescenc correlation spectroscopy. The intracellular mobility of NLS cargoes and choose their import receptor proteins. FCS is used to measure the intracellular dynamics of the nuclear import cargoes and import receptors proteins, karyopherin-alpha and karyopherin-beta and representative NLS cargoes, each expressed in living cells as an enhanced eGFP fusion protein.

Studies shows that for each of the fusion proteins, the anomalous subdiffusion model fit the measured correlation curves best, both in nucleus and in the cytoplasm, as judged by reduced chi-square analysis.

Nuclear protein import is a selective process. These short stretches of amino acids interact with proteins located in the cytoplasm, on the nuclear envelope, and/or the nuclear pore complex. Following binding at the pore complex, proteins are translocated through the pore into the nucleus in a manner requiring ATP. The nuclear receptors, like all cellular proteins, are synthesized on ribosomes that reside outside the nucleus. Import of the nuclear receptors into the nucleus requires the NLS, which is located near the border of C and D domains. As a result of their NLSs , most of the nuclear receptors reside in the nucleus, with or without their ligands. Nuclear import of several transcription factors mediated by importin alpha through binding of their NLS. Other transcription factors response elements binding proteins and activator protein1 bind directly to importin beta through their NLS.

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