Caponigro G, Parker R
Department of Molecular and Cellular Biology, University of Arizona, Tucson 85721, USA.
Nucleic Acids Res. 1996 Nov 1;24(21):4304-12. doi: 10.1093/nar/24.21.4304.
The decay rates of eukaryotic transcripts can be determined by sequence elements within an mRNA. One example of this phenomenon is the rapid degradation of the yeast MATalpha1 mRNA, which is promoted by a 65 nt segment of its coding region termed the MATalpha1 instability element (MIE). The MIE is also capable of destabilizing the stable PGK1 transcript. To determine how the MIE accelerates mRNA turnover we examined the mechanism of degradation of the MATalpha1 transcript. These experiments indicated that the MATalpha1 mRNA was degraded by a deadenylation-dependent decapping reaction which exposed the transcript to 5'-->3' exonucleolytic digestion. Deletion of the MIE from the MATalpha1 mRNA decreased the rate at which this mRNA was decapped. In contrast, insertion of the MIE into the PGK1 transcript caused an increase in the rate of deadenylation of the resulting chimeric mRNA. These observations suggest that the MIE promotes rapid mRNA decay by increasing the rates of deadenylation and decapping, with its primary effect on mRNA turnover depending on additional features of a given transcript. These results also strengthen the hypothesis that deadenylation-dependent decapping is a common pathway of mRNA decay in yeast and indicate that an instability element within the coding region of an mRNA can effect nucleolytic events that occur at both the 5'- and 3'-ends of an mRNA.
真核转录本的降解速率可由mRNA内的序列元件决定。这种现象的一个例子是酵母MATalpha1 mRNA的快速降解，其由编码区的一个65个核苷酸的片段（称为MATalpha1不稳定元件，MIE）所促进。MIE也能够使稳定的PGK1转录本不稳定。为了确定MIE如何加速mRNA周转，我们研究了MATalpha1转录本的降解机制。这些实验表明，MATalpha1 mRNA通过依赖去腺苷酸化的脱帽反应被降解，该反应使转录本暴露于5'→3'核酸外切酶消化。从MATalpha1 mRNA中删除MIE降低了该mRNA脱帽的速率。相反，将MIE插入PGK1转录本导致所得嵌合mRNA的去腺苷酸化速率增加。这些观察结果表明，MIE通过增加去腺苷酸化和脱帽的速率来促进mRNA的快速降解，其对mRNA周转的主要影响取决于给定转录本的其他特征。这些结果也强化了这样的假设，即依赖去腺苷酸化的脱帽是酵母中mRNA降解的常见途径，并表明mRNA编码区内的不稳定元件可影响在mRNA 5'端和3'端发生的核酸水解事件。
