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首页> 外文期刊>Molecular and Cellular Biology >Determinants of mRNA stability in Dictyostelium discoideum amoebae: differences in poly(A) tail length, ribosome loading, and mRNA size cannot account for the heterogeneity of mRNA decay rates.
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Determinants of mRNA stability in Dictyostelium discoideum amoebae: differences in poly(A) tail length, ribosome loading, and mRNA size cannot account for the heterogeneity of mRNA decay rates.

机译：盘基网柄菌中mRNA稳定性的决定因素：聚（A）尾巴长度，核糖体负载和mRNA大小的差异不能解释mRNA衰减率的异质性。

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As an approach to understanding the structures and mechanisms which determine mRNA decay rates, we have cloned and begun to characterize cDNAs which encode mRNAs representative of the stability extremes in the poly(A)+ RNA population of Dictyostelium discoideum amoebae. The cDNA clones were identified in a screening procedure which was based on the occurrence of poly(A) shortening during mRNA aging. mRNA half-lives were determined by hybridization of poly(A)+ RNA, isolated from cells labeled in a 32PO4 pulse-chase, to dots of excess cloned DNA. Individual mRNAs decayed with unique first-order decay rates ranging from 0.9 to 9.6 h, indicating that the complex decay kinetics of total poly(A)+ RNA in D. discoideum amoebae reflect the sum of the decay rates of individual mRNAs. Using specific probes derived from these cDNA clones, we have compared the sizes, extents of ribosome loading, and poly(A) tail lengths of stable, moderately stable, and unstable mRNAs. We found (i) no correlation between mRNA size and decay rate; (ii) no significant difference in the number of ribosomes per unit length of stable versus unstable mRNAs, and (iii) a general inverse relationship between mRNA decay rates and poly(A) tail lengths. Collectively, these observations indicate that mRNA decay in D. discoideum amoebae cannot be explained in terms of random nucleolytic events. The possibility that specific 3'-structural determinants can confer mRNA instability is suggested by a comparison of the labeling and turnover kinetics of different actin mRNAs. A correlation was observed between the steady-state percentage of a given mRNA found in polysomes and its degree of instability; i.e., unstable mRNAs were more efficiently recruited into polysomes than stable mRNAs. Since stable mRNAs are, on average, "older" than unstable mRNAs, this correlation may reflect a translational role for mRNA modifications that change in a time-dependent manner. Our previous studies have demonstrated both a time-dependent shortening and a possible translational role for the 3' poly(A) tracts of mRNA. We suggest, therefore, that the observed differences in the translational efficiency of stable and unstable mRNAs may, in part, be attributable to differences in steady-state poly(A) tail lengths.
机译：作为理解决定mRNA衰变速率的结构和机制的一种方法，我们已经克隆并开始表征cDNA，这些cDNA编码盘状双歧杆菌的poly（A）+ RNA群体中代表极端稳定性的mRNA。通过基于mRNA衰老过程中poly（A）缩短的筛选过程，鉴定了cDNA克隆。通过从32PO4脉冲追踪标记的细胞中分离的poly（A）+ RNA与过量克隆的DNA点杂交来确定mRNA的半衰期。单个mRNA的衰变速率在0.9到9.6 h之间，具有唯一的一阶衰变速率，这表明变形衣原盘虫中总poly（A）+ RNA的复杂衰变动力学反映了单个mRNA衰变速率的总和。使用衍生自这些cDNA克隆的特定探针，我们比较了稳定，中度稳定和不稳定mRNA的大小，核糖体负载量和poly（A）尾长。我们发现（i）mRNA大小与衰减率之间没有相关性; （ii）稳定和不稳定mRNA的每单位长度核糖体数量无显着差异，并且（iii）mRNA衰减率与poly（A）尾巴长度之间存在一般的反比关系。总体而言，这些观察结果表明，不能用随机的溶核事件来解释变形虫D. discoideum amoebae中的mRNA衰减。通过比较不同肌动蛋白mRNA的标记和周转动力学，暗示了特定的3'结构决定簇可以赋予mRNA不稳定性的可能性。在多核糖体中发现的给定mRNA的稳态百分比与其不稳定程度之间存在相关性。即，不稳定的mRNA比稳定的mRNA更有效地募集到多核糖体中。由于稳定的mRNA平均比不稳定的mRNA“老”，因此这种相关性可能反映了以时间依赖性方式变化的mRNA修饰的翻译作用。我们以前的研究表明，mRNA的3'poly（A）片段既有时间依赖性的缩短作用，又有可能的翻译作用。因此，我们建议，观察到的稳定和不稳定mRNA的翻译效率差异可能部分归因于稳态poly（A）尾巴长度的差异。

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