非编码RNA分类
非编码RNA (non-coding RNA，ncRNA)指不翻译成多肽的RNA。按照长度不同，短于200nt的归为小非编码RNA (small non-coding RNAs，sncRNAs)，长于200nt的归为长非编码RNA (long non-coding RNAs，lncRNAs)。
在整个人类基因组中，有超过 90%的基因组序列都会转录出来，但是令人惊讶的是只有不到*2%的转录本会被翻译成氨基酸。其余的均为非编码 RNA (Non-coding RNA, ncRNA) (Brosnan and Voinnet 2009; Consortium 2012a)。
根据其分子大小，非编码 RNA 中参与生物体调控的主要有两大类 ：短链非编码 RNA（包含 small RNA、microRNA 和 pi RNA 等）和长链非编码 RNA (long non-coding RNA， lncRNA)。lncRNA) 是一类长度介于 200 nt-100000 nt 之间，但是不具备编码蛋白能力或者很少编码蛋白的 RNA 片段。
lncRNA分类：
LncRNA 根据其是否与蛋白编码序列重叠可被分为位于基因间区的 lncRNA（lincRNA），内含子区 lncRNA，正义 lncRNA，天然反义lncRNA 和双向 lncRNA(Mercer et al 2009) 。
来源：
这些 lncRNAs 位于基因与基因之间，是一类独立存在的转录本，大多由 RNA 聚合酶 II 转录，具有典型的 ployA 尾巴。
其他sncRNA
circular RNA (circRNA): 200-2000bp, the main length distribution is about 500 bp
competing endogenous RNAs(ceRNA):Sharing transcripts of the binding sites of microRNAs,competing to bind to the same microRNAs.Normally lncRNA and circRNA compete to bind to microRNAs. We call lncRNA and circRNA ceRNA.
Major Classes of Small Noncoding RNAs
| Class | Size | Biogenesis | Number of Members (humans) | Function |
|---|---|---|---|---|
| microRNA(miRNA) | 21-23 nt | Processed by DICER from 65 to 70 nt precursors | >2500 | Regulation of gene expression |
| piwi-RNA(piRNA) | 25-33 nt | Nuclear precursor amplified by ping pong mechanism in cytoplasm | >20,000 | Regulation of gene expression |
| Endogenous silencing RNA(endo-siRNA) | 21-26 nt | Processed from messager RNA transcripts | Unknown | Regulation of gene expression |
| Small nucleolar RNA(snoRNA) | 60-300 nt | Processed from messager RNA introns | >260 | Particpates chemical modification of other RNAs |
| Small nuclear RNA (snRNA) | 150 nt | RNA polymerase II and III | 9 families | Particpates in splicing of other RNAs |
| Transfer RNA(tRNA) | 73-93 nt | RNA polymerase III | >500 | Translation of mRNA to protein |
| microRNA off-setRNA(moRNA) | 19-23 nt | Processed from miRNA precursor | Unknown | Unknown |
| Enhancer RNA(eRNA) | 50-2000 nt | Nascent RNA transcription | >2000 | Regulation proximal gene expression |
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