张筱晨， 周 惠， 屈良鹄*
(中山大学生物工程研究中心，广州510275)
摘　要：核仁小分子RNA(snoRNA)是一类广泛分布于真核生物细胞核仁的小分子非编码RNA，具有保守的结构元件，并以此划分为3 大类：box C/D snoRNA、box H/ACA snoRNA 和MRP RNA。其中box C/D 和box H/ACA 是已知snoRNA 的主要类型，以碱基配对的方式分别指导着核糖体RNA 的甲基化和假尿嘧啶化修饰。研究发现，snoRNA 除了在核糖体RNA 的生物合成中发挥作用之外，还能够指导snRNA、tRNA 和mRNA 的转录后修饰。此外，还有相当数量的snoRNA 功能不明，被称为孤儿snoRNA(orphan snoRNA)。在哺乳动物的孤儿snoRNA 中，印迹snoRNA(imprinted snoRNA)是最为特殊的一群，由基因组印迹区编码，具有明显的组织表达特异性。原核生物古细菌中类snoRNA 的鉴定表明这些非编码RNA 家族成员的古老起源；而哺乳动物中大量的snoRNA 反转座子的存在更为人们探索snoRNA 在基因组中扩增和功能进化提供了新的思路。
关键词：snoRNA；基因组印迹；snoRNA 反转座子
中图分类号：Q752; Q522　　文献标识码：A
Structure and function of snoRNAs
ZHANG Xiao-chen, ZHOU Hui, QU Liang-hu*
(Biotechnology Research Center, Sun Yat-Sen University, Guangzhou 510275, China)
Abstract: Small nucleolar RNAs (snoRNAs) represent an abundant group of noncoding RNAs with existence in the nucleolus of eukaryotes. Based on the conserved structure elements, the majority of snoRNAs can be divided into two families, box C/D snoRNAs and box H/ACA snoRNAs, which function on 2' -O- methylation and pseudouridylation of rRNA, respectively, through the formation of a canonical guide RNA duplex at the modification site. However, recent studies show that the complexity of the two snoRNA guide families is far beyond expectation. Dozes of novel snoRNAs target other cellular RNAs, including snRNAs, tRNAs and even mRNAs. In addition, an increasing number of orphan snoRNAs without known targets were identified, and remarkably, imprinted snoRNAs were among them, which are encoded by genomic imprinting region and expressed in a tissue-specific pattern. Furthermore, the ancient origin of these noncoding RNA families was reflected by the identification of snoRNA homologs in Archaea, and latest characterization of snoRNA retrogenes offers new perspectives to their proliferation and evolution.
Key words: snoRNA; genomic imprinting; snoRNA retrogene