Adami G R, Carmichael G G
Nucleic Acids Res. 1987 Mar 25;15(6):2593-610. doi: 10.1093/nar/15.6.2593.
Polyoma virus late RNA processing provides a convenient model system in which to study the mechanics of splicing in vivo. In order to understand further the role of the untranslated "late leader" unit in late RNA processing we have constructed a group of polyoma viruses with deletions and substitutions in the leader exon. This has allowed us to determine that there is a minimum exon size required for both pre-mRNA splicing and stability in this system. We show here that the non-viability of a mutant (ALM) with a 9 base late leader unit is due to a general defect in late RNA splicing. In addition, ALM-infected cells show at least 40-fold depression in the accumulation of late nuclear RNA (spliced or unspliced). The ALM late promoter, however, functions nearly normally. Substituted leader variants with 51- to 96-base long exons of unrelated sequence are viable (G. Adami and G. Carmichael, J. Virol. 58, 417-425, 1986). We show here that late RNA from one of these substituted leader mutants (containing a 51-base leader exon) is spliced at wild type levels, with virtually no defect in accumulation. Thus, in the polyoma system, splice sites separated by only 9 bases can inhibit each others usage, presumably by steric interference. We suggest that this type of inhibition leads to extreme RNA instability.
多瘤病毒晚期RNA加工提供了一个方便的模型系统，可用于研究体内剪接机制。为了进一步了解未翻译的“晚期前导序列”单元在晚期RNA加工中的作用，我们构建了一组在前导外显子中有缺失和替换的多瘤病毒。这使我们能够确定在该系统中，前体mRNA剪接和稳定性所需的外显子最小大小。我们在此表明，具有9个碱基的晚期前导序列单元的突变体（ALM）的非生存能力是由于晚期RNA剪接中的普遍缺陷。此外，感染ALM的细胞在晚期核RNA（剪接或未剪接）的积累中显示至少40倍的降低。然而，ALM晚期启动子的功能几乎正常。具有不相关序列的51至96个碱基长外显子的取代前导变体是可行的（G.阿达米和G.卡迈克尔，《病毒学杂志》58，417 - 425，1986）。我们在此表明，来自这些取代前导突变体之一（包含51个碱基的前导外显子）的晚期RNA以野生型水平进行剪接，在积累方面几乎没有缺陷。因此，在多瘤病毒系统中，仅相隔9个碱基的剪接位点可能会通过空间干扰相互抑制使用。我们认为这种类型的抑制会导致RNA极度不稳定。
