Using Yeast to Study Exchange of Macromolecules between the Cytoplasm and the Nucleus
Research over the past ten years has yielded information about the mechanism and some of the factors required for the specific uptake of certain proteins by the nucleus (see, for example, Garcia-Bustos et al., 1991; Silver, 1991; Stochaj and Silver, 1992 for recent review). Proteins move from their site of synthesis in the cytoplasm to the nuclear envelope. Specific targeting to the nucleus is accomplished in some cases by the presence of a short stretch of amino acids on the nuclear-destined proteins, termed an NLS for nuclear localization sequence. The NLS may mediate the interaction of the transported protein with cytoplasmic carriers or “receptors.” We know that proteins enter the nucleus via an aqueous channel formed by a complex of proteins in the nuclear envelope (termed the NPC for nuclear pore complex [Feldherr et al., 1984]). NLS-containing proteins may pass through the pore in association with the receptor or released from the receptor at the pore entry. The import process has been shown to require ATP in animal cells, Xenopus oocytes and yeast (Newmeyer and Forbes, 1988; Richardson et al., 1988; Breeuwer and Goldfarb, 1990; Garcia-Bustos et al., 1991).
KeywordsNuclear Protein Nuclear Envelope Nuclear Localization Signal Nuclear Import Nuclear Pore Complex
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