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核糖體生物發生對於細胞代謝至關重要,並且對疾病和衰老具有重要意義。人神經膠質瘤抑癌候選基因2(GLTSCR2)和酵母(Saccharomyces cerevisiae)核仁蛋白53(Nop53)是直系同源蛋白,具有核糖體生物發生因子(RBFs)的功能;敲低GLTSCR2會損害18S和5.8S核糖體RNA(rRNA)的成熟,而Nop53是5.8S和25S rRNA的成熟所必需的。
在這裡,我們在擬南芥鑑定克隆到了與人類GLTSCR2和酵母Nop53同源基因SMO4, SMO4的功能喪失導致輕度的形態表型。然而,我們發現smo4突變體表現出核仁肥大和組織紊亂,5.8S和18S rRNA前體的過度積累以及40S:60S核糖體亞基比例失衡。像酵母Nop53和人GLTSCR2一樣,擬南芥SMO4參與5.8S rRNA成熟。在酵母中,Nop53與mRNA轉運4(Mtr4)協同作用,使5.8S rRNA成熟。在擬南芥中,我們發現SMO4在5.8S rRNA成熟途徑中的作用與針對MTR4所述的相似。但是,SMO4似乎不像MTR4那樣參與45S pre-rRNA的5'-ETS衍生的副產物的降解。
Ribosome biogenesis is crucial for cellular metabolism and has important implications for disease and aging. Human glioma tumor-suppressor candidate region gene 2 (GLTSCR2) and yeast (Saccharomyces cerevisiae) Nucleolar protein 53 (Nop53) are orthologous proteins with demonstrated roles as ribosome biogenesis factors (RBFs); knockdown of GLTSCR2 impairs maturation of 18S and 5.8S ribosomal RNAs (rRNAs), and Nop53 is required for maturation of 5.8S and 25S rRNAs. Here, we characterized SMALL ORGAN 4 (SMO4), the most likely ortholog of human GLTSCR2 and yeast Nop53 in Arabidopsis (Arabidopsis thaliana). Loss of function of SMO4 results in a mild morphological phenotype; however, we found that smo4 mutants exhibit strong cytological and molecular phenotypes: nucleolar hypertrophy and disorganization, overaccumulation of 5.8S and 18S rRNA precursors, and an imbalanced 40S:60S ribosome subunit ratio. Like yeast Nop53 and human GLTSCR2, Arabidopsis SMO4 participates in 5.8S rRNA maturation. In yeast, Nop53 cooperates with mRNA transport 4 (Mtr4) for 5.8S rRNA maturation. In Arabidopsis, we found that SMO4 plays similar roles in the 5.8S rRNA maturation pathway than those described for MTR4. However, SMO4 seems not participate in the degradation of by-products derived from the 5′-ETS of 45S pre-rRNA, as MTR4 does.
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