Kallstrom George, Hedges John, Johnson Arlen
Section of Molecular Genetics and Microbiology and Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas 78712, USA.
Mol Cell Biol. 2003 Jun;23(12):4344-55. doi: 10.1128/MCB.23.12.4344-4355.2003.
We characterized two essential putative GTPases, Nog1p and Lsg1p, that are found associated with free 60S ribosomal subunits affinity purified with the nuclear export adapter Nmd3p. Nog1p and Lsg1p are nucleolar and cytoplasmic, respectively, and are not simultaneously on the same particle, reflecting the path of Nmd3p shuttling in and out of the nucleus. Conditional mutants of both NOG1 and LSG1 are defective in 60S subunit biogenesis and display diminished levels of 60S subunits at restrictive temperature. Mutants of both genes also accumulate the 60S ribosomal reporter Rpl25-eGFP in the nucleolus, suggesting that both proteins are needed for subunit export from the nucleolus. Since Lsg1p is cytoplasmic, its role in nuclear export is likely to be indirect. We suggest that Lsg1p is needed to recycle an export factor(s) that shuttles from the nucleus associated with the nascent 60S subunit.
我们鉴定了两个必需的假定GTP酶，即Nog1p和Lsg1p，它们与通过核输出衔接蛋白Nmd3p亲和纯化的游离60S核糖体亚基相关。Nog1p和Lsg1p分别定位于核仁与细胞质，且不会同时存在于同一个颗粒上，这反映了Nmd3p穿梭进出细胞核的路径。NOG1和LSG1的条件突变体在60S亚基生物合成方面存在缺陷，并且在限制温度下60S亚基水平降低。这两个基因的突变体还会在核仁中积累60S核糖体报告蛋白Rpl25-eGFP，表明这两种蛋白质都是亚基从核仁输出所必需的。由于Lsg1p位于细胞质中，其在核输出中的作用可能是间接的。我们认为Lsg1p对于循环利用与新生60S亚基相关的从细胞核穿梭出来的一种或多种输出因子是必需的。
