Godfrey Ashley C, White Anne E, Tatomer Deirdre C, Marzluff William F, Duronio Robert J
Department of Biology, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
RNA. 2009 Sep;15(9):1661-72. doi: 10.1261/rna.1518009. Epub 2009 Jul 20.
Metazoan replication-dependent histone mRNAs are not polyadenylated, and instead terminate in a conserved stem-loop structure generated by an endonucleolytic cleavage of the pre-mRNA involving U7 snRNP. U7 snRNP contains two like-Sm proteins, Lsm10 and Lsm11, which replace SmD1 and SmD2 in the canonical heptameric Sm protein ring that binds spliceosomal snRNAs. Here we show that mutations in either the Drosophila Lsm10 or the Lsm11 gene disrupt normal histone pre-mRNA processing, resulting in production of poly(A)+ histone mRNA as a result of transcriptional read-through to cryptic polyadenylation sites present downstream from each histone gene. This molecular phenotype is indistinguishable from that which we previously described for mutations in U7 snRNA. Lsm10 protein fails to accumulate in Lsm11 mutants, suggesting that a pool of Lsm10-Lsm11 dimers provides precursors for U7 snRNP assembly. Unexpectedly, U7 snRNA was detected in Lsm11 and Lsm1 mutants and could be precipitated with anti-trimethylguanosine antibodies, suggesting that it assembles into a snRNP particle in the absence of Lsm10 and Lsm11. However, this U7 snRNA could not be detected at the histone locus body, suggesting that Lsm10 and Lsm11 are necessary for U7 snRNP localization. In contrast to U7 snRNA null mutants, which are viable, Lsm10 and Lsm11 mutants do not survive to adulthood. Because we cannot detect differences in the histone mRNA phenotype between Lsm10 or Lsm11 and U7 mutants, we propose that the different terminal developmental phenotypes result from the participation of Lsm10 and Lsm11 in an essential function that is distinct from histone pre-mRNA processing and that is independent of U7 snRNA.
后生动物中依赖复制的组蛋白mRNA不进行多聚腺苷酸化，而是在由前体mRNA的内切核酸酶切割产生的保守茎环结构处终止，该切割过程涉及U7 snRNP。U7 snRNP包含两种类Sm蛋白，Lsm10和Lsm11，它们在结合剪接体snRNA的典型七聚体Sm蛋白环中取代了SmD1和SmD2。在这里，我们表明果蝇Lsm10或Lsm11基因中的突变会破坏正常的组蛋白前体mRNA加工，由于转录通读至每个组蛋白基因下游存在的隐蔽多聚腺苷酸化位点，导致产生多聚(A)+组蛋白mRNA。这种分子表型与我们之前描述的U7 snRNA突变的表型无法区分。Lsm10蛋白在Lsm11突变体中无法积累，这表明一组Lsm10-Lsm11二聚体为U7 snRNP组装提供前体。出乎意料的是，在Lsm11和Lsm1突变体中检测到了U7 snRNA，并且可以用抗三甲基鸟苷抗体沉淀，这表明它在没有Lsm10和Lsm11的情况下组装成snRNP颗粒。然而，在组蛋白基因座体处未检测到这种U7 snRNA，这表明Lsm10和Lsm11对于U7 snRNP定位是必需的。与可存活的U7 snRNA无效突变体相反，Lsm10和Lsm11突变体无法存活至成年期。由于我们无法检测到Lsm10或Lsm11与U7突变体之间组蛋白mRNA表型的差异，我们提出不同的终末发育表型是由于Lsm10和Lsm11参与了一种与组蛋白前体mRNA加工不同且独立于U7 snRNA的基本功能。
