Leverette R D, Andrews M T, Maxwell E S
Department of Biochemistry, North Carolina State University, Raleigh 27695.
Cell. 1992 Dec 24;71(7):1215-21. doi: 10.1016/s0092-8674(05)80069-8.
U14 snRNA is a small nucleolar RNA species essential for eukaryotic pre-rRNA processing. We have previously shown that the mouse U14 snRNA genes are positioned within introns 5, 6, and 8 on the coding strand of the constitutively expressed cognate hsc70 heat shock gene. This genomic organization suggested the possibility that U14 snRNAs are transcribed as part of the hsc70 pre-mRNA and then excised from the intron to yield mature U14 snRNA species. To test this hypothesis directly, we have microinjected Xenopus oocytes with hsc70 pre-mRNA transcripts possessing intron 5 and the encoded U14 snRNA sequence. Processing results demonstrate that, in addition to the splicing of upstream and downstream exons, a mature 87 nt U14 snRNA is excised from the intron. Accurate excision of U14 snRNA from hsc70 intron 5 can occur in the absence of splicing. These results demonstrate a biosynthetic pathway for an snRNA species and provide a novel example of a eukaryotic pre-mRNA intron that is processed to produce a stable, biologically functional RNA species.
U14小核仁RNA是真核生物前体核糖体RNA加工所必需的一种小核仁RNA。我们之前已经表明，小鼠U14小核仁RNA基因位于组成型表达的同源热休克蛋白70（hsc70）热休克基因编码链的第5、6和8个内含子内。这种基因组组织提示了一种可能性，即U14小核仁RNA作为hsc70前体信使RNA的一部分被转录，然后从内含子中切除以产生成熟的U14小核仁RNA。为了直接验证这一假设，我们向非洲爪蟾卵母细胞显微注射了含有第5个内含子和编码的U14小核仁RNA序列的hsc70前体信使RNA转录本。加工结果表明，除了上游和下游外显子的剪接外，一个成熟的87个核苷酸的U14小核仁RNA从内含子中被切除。在没有剪接的情况下，U14小核仁RNA也能从hsc70的第5个内含子中准确切除。这些结果证明了一种小核仁RNA的生物合成途径，并提供了一个真核生物前体信使RNA内含子被加工以产生一种稳定的、具有生物学功能的RNA的新例子。
