Crispino J D, Mermoud J E, Lamond A I, Sharp P A
Massachusetts Institute of Technology, Department of Biology, Cambridge 02139-4307, USA.
RNA. 1996 Jul;2(7):664-73.
We have identified a class of pre-mRNAs that are spliced in HeLa extracts depleted for U1 snRNP (delta U1 extracts). Previously, we described pre-mRNAs that can be spliced in delta U1 extracts only when high concentrations of SR splicing factors are added. In contrast, the substrates characterized here are efficiently processed in delta U1 extracts without the addition of excess SR proteins. The members of this class comprise both a naturally occurring pre-mRNA, from the Drosophila fushi tarazu gene, and a chimera containing sequences from two different pre-mRNAs that individually are dependent upon U1 snRNP or excess SR proteins. Several sequence elements account for the variations in dependence on U1 snRNP and SR proteins for splicing. In one pre-mRNA, a single element was identified adjacent to the branch site. In the other, two elements flanking the 5' splice site were found to be critical. This U1-independent splicing reaction may provide a mechanism for cells to control the extent of processing of different classes of pre-mRNAs in response to altered activities of SR proteins, and furthermore suggests that U1 snRNP-independent splicing may not be uncommon.
我们已经鉴定出一类在前体mRNA在缺乏U1 snRNP的HeLa细胞提取物（δU1提取物）中进行剪接。此前，我们描述过一些前体mRNA，它们只有在添加高浓度的SR剪接因子时才能在δU1提取物中进行剪接。相比之下，这里所描述的底物在不添加过量SR蛋白的δU1提取物中就能高效加工。这类成员包括来自果蝇分节基因的天然前体mRNA，以及一个包含来自两个不同前体mRNA序列的嵌合体，这两个前体mRNA单独存在时依赖U1 snRNP或过量的SR蛋白。几个序列元件导致了剪接对U1 snRNP和SR蛋白依赖的差异。在一个前体mRNA中，在分支位点附近鉴定出一个单一元件。在另一个中，发现5'剪接位点两侧的两个元件至关重要。这种不依赖U1的剪接反应可能为细胞提供一种机制，以响应SR蛋白活性的改变来控制不同类别的前体mRNA的加工程度，此外还表明不依赖U1 snRNP的剪接可能并不罕见。
