Kressler D, Rojo M, Linder P, Cruz J
Département de Biochimie Médicale, Centre Médical Universitaire, Université de Genève, 1 rue Michel-Servet, 1211 Genève 4, Switzerland.
Nucleic Acids Res. 1999 Dec 1;27(23):4598-608. doi: 10.1093/nar/27.23.4598.
Several mutants ( spb1 - spb7 ) have been previously identified as cold-sensitive extragenic suppressors of loss-of-function mutations in the poly(A)(+)-binding protein 1 of Saccharomyces cerevisiae. Cloning, sequence and disruption analyses revealed that SPB1 (YCL054W) encodes an essential putative S -adenosylmethionine-dependent methyltransferase. Polysome analyses showed an under-accumulation of 60S ribosomal subunits in the spb1-1 mutant and in a strain genetically depleted of Spb1p. Northern and primer extension analyses indicated that this was due to inhibition of processing of the 27SB precursors, which results in depletion of the mature 25S and 5.8S rRNAs. At later time points of Spb1p depletion, the stability of 40S ribosomal subunits is also affected. These results suggest that Spb1p is involved in 60S ribosomal subunit biogenesis and associates early with the pre-ribosomes. Consistent with this, hemagglutinin epitope-tagged Spb1p localizes to the nucleus with nucleolar enrichment. Despite the expected methyltransferase activity of Spb1p, global methylation of pre-rRNA is not affected upon Spb1p depletion. We propose that Spb1p is required for proper assembly of pre-ribosomal particles during the biogenesis of 60S ribosomal subunits.
先前已鉴定出几种突变体（spb1 - spb7），它们是酿酒酵母多聚腺苷酸（+）结合蛋白1功能丧失突变的冷敏感基因外抑制子。克隆、序列和缺失分析表明，SPB1（YCL054W）编码一种必需的假定S -腺苷甲硫氨酸依赖性甲基转移酶。多核糖体分析显示，在spb1-1突变体和基因缺失Spb1p的菌株中，60S核糖体亚基积累不足。Northern和引物延伸分析表明，这是由于27SB前体加工受到抑制，导致成熟的25S和5.8S rRNA减少。在Spb1p缺失的后期，40S核糖体亚基的稳定性也受到影响。这些结果表明，Spb1p参与60S核糖体亚基的生物合成，并早期与前核糖体结合。与此一致的是，血凝素表位标签化的Spb1p定位于细胞核并富集于核仁。尽管Spb1p具有预期的甲基转移酶活性，但Spb1p缺失时前体rRNA的整体甲基化不受影响。我们提出，Spb1p是60S核糖体亚基生物合成过程中前核糖体颗粒正确组装所必需的。
