Craig S P, Muralidhar M G, McKerrow J H, Wang C C
Department of Pharmaceutical Chemistry, University of California, San Francisco 94143.
Nucleic Acids Res. 1989 Feb 25;17(4):1635-47. doi: 10.1093/nar/17.4.1635.
The single copy gene for the hypoxanthine-guanine phosphoribosyltransferase (HGPRTase) of the parasitic trematode, Schistosoma mansoni, contains seven introns, the first four of which are only 31, 33, 42, and 32 bases in length. These are the smallest introns ever discovered in a non-viral nuclear gene coding for protein. These very small introns possess the canonical GT...AG splice site sequences but lack the branching sequence, the secondary structure, and the minimum size of approximately 50 bases believed to be required for the splicing of eucaryotic mRNA precursors. Evidently, a somewhat different splicing mechanism for the transcripts of these very small introns is necessary. Their discovery within the genes of helminths raises theoretical considerations for the evolution of introns in eucaryotes.
寄生吸虫曼氏血吸虫的次黄嘌呤 - 鸟嘌呤磷酸核糖转移酶（HGPRTase）单拷贝基因含有7个内含子，其中前4个内含子长度仅为31、33、42和32个碱基。这些是在编码蛋白质的非病毒核基因中发现的最小内含子。这些非常小的内含子具有典型的GT...AG剪接位点序列，但缺乏分支序列、二级结构以及真核生物mRNA前体剪接所需的约50个碱基的最小尺寸。显然，对于这些非常小的内含子的转录本，需要一种略有不同的剪接机制。它们在蠕虫基因中的发现引发了关于真核生物内含子进化的理论思考。
