Microbiology and Molecular Genetics Department, University of Texas Health Science Center at Houston, Houston, Texas 77030.
Microbiology and Molecular Genetics Department, University of Texas Health Science Center at Houston, Houston, Texas 77030
Genetics. 2020 Dec;216(4):1051-1069. doi: 10.1534/genetics.120.303641. Epub 2020 Sep 30.
Faithful degradation of mRNAs is a critical step in gene expression, and eukaryotes share a major conserved mRNA decay pathway. In this major pathway, the two rate-determining steps in mRNA degradation are the initial gradual removal of the poly(A) tail, followed by removal of the cap structure. Removal of the cap structure is carried out by the decapping enzyme, containing the Dcp2 catalytic subunit. Although the mechanism and regulation of mRNA decay is well understood, the consequences of defects in mRNA degradation are less clear. Dcp2 has been reported as either essential or nonessential. Here, we clarify that Dcp2 is not absolutely required for spore germination and extremely slow growth, but in practical terms it is impossible to continuously culture ∆ under laboratory conditions without suppressors arising. We show that null mutations in at least three different genes are each sufficient to restore growth to a ∆, of which ∆ and ∆ appear the most specific. We show that ∆ and ∆ suppress by mechanisms that are different from each other and from previously isolated suppressors. The suppression mechanism for is determined by the unique GAG anticodon of this tRNA, and thus likely by translation of some CUC or CUU codons. Unlike previously reported suppressors of decapping defects, these suppressors do not detectably restore decapping or mRNA decay to normal rates, but instead allow survival while only modestly affecting RNA homeostasis. These results provide important new insight into the importance of decapping, resolve previously conflicting publications about the essentiality of , provide the first phenotype for a mutant, and show that multiple distinct mechanisms can bypass Dcp2 requirement.
mRNA 的忠实降解是基因表达的关键步骤，真核生物共享主要保守的 mRNA 降解途径。在这个主要途径中，mRNA 降解的两个限速步骤是聚（A）尾的初始逐渐去除，然后是帽结构的去除。帽结构的去除由含有 Dcp2 催化亚基的脱帽酶完成。尽管 mRNA 降解的机制和调控已经得到很好的理解，但 mRNA 降解缺陷的后果还不太清楚。已经报道 Dcp2 要么是必需的，要么是非必需的。在这里，我们澄清 Dcp2 对于孢子萌发和极其缓慢的生长并不是绝对必需的，但实际上在没有抑制剂出现的情况下，在实验室条件下连续培养 ∆ 是不可能的。我们表明，至少三种不同基因的 null 突变都足以使 ∆ 恢复生长，其中 ∆ 和 ∆ 似乎最具特异性。我们表明， ∆ 和 ∆ 通过与彼此以及与先前分离的 抑制剂不同的机制来抑制 。该 tRNA 的独特 GAG 反密码子决定了 的抑制机制，因此可能是翻译某些 CUC 或 CUU 密码子。与以前报道的脱帽缺陷抑制剂不同，这些抑制剂不会显著恢复脱帽或 mRNA 降解至正常速率，而是在仅适度影响 RNA 稳态的情况下允许存活。这些结果为脱帽的重要性提供了重要的新见解，解决了以前关于 必需性的相互矛盾的出版物，为 突变体提供了第一个表型，并表明多种不同的机制可以绕过 Dcp2 的需求。
