Multiple regions of NSR1 are sufficient for accumulation of a fusion protein within the nucleolus.
Multiple regions of NSR1 are sufficient for accumulation of a fusion protein within the nucleolus.
复制标题
NSR1 的多个区域足以在核仁内积累融合蛋白。
DOI：
10.1083/jcb.123.5.1081
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发表时间：
1993
期刊：
影响因子：
--
通讯作者：
Mélèse,T
中科院分区：
文献类型：
--
作者：
Yan,C;Mélèse,T
NSR1, a 67-kD nucleolar protein, was originally identified in our laboratory as a nuclear localization signal binding protein, and has subsequently been found to be involved in ribosome biogenesis. NSR1 has three regions: an acidic/serine-rich NH2 terminus, two RNA recognition motifs, and a glycine/argininerich COOH terminus. In this study we show that NSR1 itself has a bipartite nuclear localization sequence. Deletion of either basic amino acid stretch results in the mislocalization of NSR1 to the cytoplasm. We further demonstrate that either of two regions, the NH2 terminus or both RNA recognition motifs, are sufficient to localize a bacterial protein, B-galactosidase, to the nucleolus. Intensive deletion analysis has further defined a specific acidic/serinerich region within the NH2 terminus as necessary for nucleolar accumulation rather than nucleolar targeting. In addition, deletion of either RNA recognition motif or point mutations in one of the RNP consensus octamers results in the mislocalization of a fusion protein within the nucleus. Although the glycine/argininerich region in the COOH terminus is not sufficient to bring B-galactosidase to the nucleolus, our studies show that this domain is necessary for nucleolar accumulation when an RNP consensus octamer in one of the RNA recognition motifs is mutated. Our findings are consistent with the notion that nucleolar localization is a result of the binding interactions of various domains of NSR1 within the nucleolus rather than the presence of a specific nucleolar targeting signal.T n~ majority of nuclear proteins contain nuclear localization sequences (NLSs) that are required for their entry into the nucleus. The sequence fits the consensus Lys-Arg/Lys-X-Arg/Lys (Chelsky et al., 1989). Nuclear transport is saturable (Goldfarb et al., 1986), occurs by selective entry, and requires energy (Newmeyer et al., 1986; Markland et al., 1987; Newmeyer and Forbes, 1988; Richardson et al., 1988). Once nuclear proteins enter the nucleus, they are found in different subnuclear regions; their final destination is most likely defined by their structural and functional interactions with proteins or nucleic acids. Some examples are: the nuclear filament proteins (lamins) that play a role in nuclear cytoarchitecture are thought to attach to the nuclear envelope by binding to the surface of the inner nuclear membrane via a 54-kD protein (Bailer et al., 1991); transcription factors that activate expression of genes interact with specific DNA sequences; ribosomal proteins are found in the nucleolus where ribosomal DNA genes encod-
