U12-dependent introns are found in small numbers in most eukaryotic genomes, but their scarcity makes accurate characterisation of their properties challenging. A computational search for U12-dependent introns was performed using the draft version of the human genome sequence. Human expressed sequences confirmed 404 U12-dependent introns within the human genome, a 6-fold increase over the total number of non-redundant U12-dependent introns previously identified in all genomes. Although most of these introns had AT-AC or GT-AG terminal dinucleotides, small numbers of introns with a surprising diversity of termini were found, suggesting that many of the non-canonical introns found in the human genome may be variants of U12‐dependent introns and, thus, spliced by the minor spliceosome. Comparisons with U2-dependent introns revealed that the U12-dependent intron set lacks the ‘short intron’ peak characteristic of U2‐dependent introns. Analysis of this U12‐dependent intron set confirmed reports of a biased distribution of U12-dependent introns in the genome and allowed the identification of several alternative splicing events as well as a surprising number of apparent splicing errors. This new larger reference set of U12-dependent introns will serve as a resource for future studies of both the properties and evolution of the U12 spliceosome.
在大多数真核
生物基因组中发现的 U12 依赖性内含子数量很少,但它们的稀缺性使得准确表征其特性具有挑战性。使用人类
基因组序列草稿版本对 U12 依赖性内含子进行计算搜索。人类表达序列证实了人类
基因组内有 404 个 U12 依赖性内含子,比之前在所有
基因组中鉴定的非冗余 U12 依赖性内含子总数增加了 6 倍。尽管大多数内含子具有 AT-AC 或 GT-AG 末端二核苷酸,但仍发现了少量具有令人惊讶的末端多样性的内含子,这表明在人类
基因组中发现的许多非规范内含子可能是 U12 依赖性内含子的变体内含子,因此由小剪接体剪接。与 U2 依赖性内含子的比较表明,U12 依赖性内含子组缺乏 U2 依赖性内含子的“短内含子”峰特征。对这个 U12 依赖性内含子集的分析证实了
基因组中 U12 依赖性内含子的偏向分布的报告,并允许鉴定几个可变剪接事件以及数量惊人的明显剪接错误。这个新的更大的 U12 依赖性内含子参考集将作为未来研究 U12 剪接体的特性和进化的资源。