Yun D F, Sherman F
Department of Biochemistry, University of Rochester, School of Medicine and Dentistry, NY 14642, USA.
Proc Natl Acad Sci U S A. 1996 Aug 20;93(17):8895-900. doi: 10.1073/pnas.93.17.8895.
Several studies have indicated that degradation of certain mRNAs is tightly coupled to their translation, whereas, in contrast, other observations suggested that translation can be inhibited without changing the stability of the mRNA. We have addressed this question with the use of altered CYC1 alleles, which encode iso-1-cytochrome c in the yeast Saccharomyces cerevisiae. The cyc1-1249 mRNA, which lacks all in-frame and out-of-frame AUG triplets, was as stable as the normal mRNA. This finding established that translation is not required for the degradation of CYC1 mRNAs. Furthermore, poly(G)18 tracks were introduced within the CYC1 mRNA translated regions to block exonuclease degradation. The recovery of 3' fragments revealed that the translatable and the AUG-deficient mRNAs are both degraded 5'-->3'. Also, the increased stability of CYC1 mRNAs in xrn1-delta strains lacking Xrn1p, the major 5'-->3' exonuclease, established that the normal and AUG-deficient mRNAs are degraded by the same pathway. In addition, deadenylylation, which activates the action of Xrn1p, occurred at equivalent rates in both normal and AUG-deficient mRNAs. We conclude that translation is not required for the normal degradation of CYC1 mRNAs, and that translatable and untranslated mRNAs are degraded by the same pathway.
多项研究表明，某些mRNA的降解与其翻译紧密相关，而相比之下，其他观察结果则表明，翻译可被抑制而不改变mRNA的稳定性。我们利用酿酒酵母中编码异-1-细胞色素c的CYC1等位基因的改变来解决这个问题。缺乏所有读框内和读框外AUG三联体的cyc1-1249 mRNA与正常mRNA一样稳定。这一发现表明CYC1 mRNA的降解不需要翻译。此外，在CYC1 mRNA翻译区域内引入poly(G)18序列以阻断核酸外切酶降解。3'片段的回收显示，可翻译的和缺乏AUG的mRNA均从5'端向3'端降解。同样，在缺乏主要的5'→3'核酸外切酶Xrn1p的xrn1-δ菌株中，CYC1 mRNA稳定性的增加表明正常mRNA和缺乏AUG的mRNA通过相同途径降解。此外，激活Xrn1p作用的去腺苷酸化在正常mRNA和缺乏AUG的mRNA中以相同速率发生。我们得出结论，CYC1 mRNA的正常降解不需要翻译，可翻译和未翻译的mRNA通过相同途径降解。
