Muhlrad D, Parker R
Department of Molecular and Cellular Biology, University of Arizona, Tucson 85721.
Genes Dev. 1992 Nov;6(11):2100-11. doi: 10.1101/gad.6.11.2100.
Decay rates of individual mRNAs in the yeast Saccharomyces cerevisiae can vary by 10- to 20-fold. To determine the basis for the rapid degradation of the mRNA encoded by the yeast MFA2 gene we have used a genetic screen to isolate mutations that increase the stability of this transcript. Analysis of point mutations obtained from this screen, and of additional lesions constructed in vitro, indicated that the MFA2 3'-untranslated region (UTR) contains sequences that specify rapid mRNA decay. Moreover, the lesions that affected mRNA decay rate also affected the process of mRNA deadenylation. Mutations in one region of the 3' UTR both decreased the rate of poly(A) shortening and increased the stability of an intermediate form in the decay pathway with an oligo(A) tail (approximately 10 nucleotides). Mutations in a second region primarily increased the stability of the oligo(A) form. These results suggest that the decay of the MFA2 mRNA initiates with the shortening of the poly(A) tail and there are specific sequences within the 3' UTR that stimulate poly(A) tail shortening as well as subsequent steps in the decay pathway. Given the similarity of this decay pathway to that seen for some mammalian mRNAs, these results suggest that mRNA deadenylation may be a common mechanism of mRNA turnover.
酿酒酵母中单个mRNA的降解速率可相差10至20倍。为了确定酵母MFA2基因编码的mRNA快速降解的基础，我们利用遗传筛选来分离能增加该转录本稳定性的突变。对从该筛选中获得的点突变以及体外构建的其他损伤的分析表明，MFA2 3'非翻译区（UTR）包含指定mRNA快速降解的序列。此外，影响mRNA降解速率的损伤也影响了mRNA去腺苷酸化的过程。3'UTR一个区域的突变既降低了多聚腺苷酸（poly(A)）缩短的速率，又增加了具有寡聚腺苷酸（oligo(A)）尾（约10个核苷酸）的降解途径中一种中间形式的稳定性。第二个区域的突变主要增加了oligo(A)形式的稳定性。这些结果表明，MFA2 mRNA的降解始于poly(A)尾的缩短，并且3'UTR内存在特定序列，这些序列会刺激poly(A)尾缩短以及降解途径中的后续步骤。鉴于这种降解途径与某些哺乳动物mRNA的降解途径相似，这些结果表明mRNA去腺苷酸化可能是mRNA周转的一种常见机制。
