The Wellcome Centre for Integrative Parasitology, University of Glasgow, College of Medical, Veterinary and Life Sciences, Institute of Infection, Immunity and Inflammation, Sir Graeme Davies Building, 120 University Place, Glasgow G12 8TA, UK.
Glasgow Polyomics, University of Glasgow, Wolfson Wohl Cancer Research Centre, Garscube Estate, Switchback Rd, Bearsden G61 1QH, UK.
Nucleic Acids Res. 2019 Sep 26;47(17):9180-9197. doi: 10.1093/nar/gkz644.
Ribonucleotides represent a threat to DNA genome stability and transmission. Two types of Ribonuclease H (RNase H) excise ribonucleotides when they form part of the DNA strand, or hydrolyse RNA when it base-pairs with DNA in structures termed R-loops. Loss of either RNase H is lethal in mammals, whereas yeast survives the absence of both enzymes. RNase H1 loss is tolerated by the parasite Trypanosoma brucei but no work has examined the function of RNase H2. Here we show that loss of T. brucei RNase H2 (TbRH2A) leads to growth and cell cycle arrest that is concomitant with accumulation of nuclear damage at sites of RNA polymerase (Pol) II transcription initiation, revealing a novel and critical role for RNase H2. Differential gene expression analysis reveals limited overall changes in RNA levels for RNA Pol II genes after TbRH2A loss, but increased perturbation of nucleotide metabolic genes. Finally, we show that TbRH2A loss causes R-loop and DNA damage accumulation in telomeric RNA Pol I transcription sites, also leading to altered gene expression. Thus, we demonstrate separation of function between two nuclear T. brucei RNase H enzymes during RNA Pol II transcription, but overlap in function during RNA Pol I-mediated gene expression during host immune evasion.
核苷酸对 DNA 基因组的稳定性和传递构成威胁。两种核糖核酸酶 H（RNase H）在核糖核苷酸成为 DNA 链的一部分时将其切除，或者在 RNA 与 DNA 碱基配对形成称为 R 环的结构时将其水解。哺乳动物中任何一种 RNase H 的缺失都是致命的，而酵母在缺乏两种酶的情况下仍然能够存活。寄生虫布氏锥虫可以耐受 RNase H1 的缺失，但没有研究检查过 RNase H2 的功能。在这里，我们表明，布氏锥虫 RNase H2（TbRH2A）的缺失会导致生长和细胞周期停滞，同时在 RNA 聚合酶（Pol）II 转录起始位点积累核损伤，揭示了 RNase H2 的新的关键作用。差异基因表达分析显示，TbRH2A 缺失后 RNA Pol II 基因的 RNA 水平总体变化有限，但核苷酸代谢基因的扰动增加。最后，我们表明 TbRH2A 的缺失会导致端粒 RNA Pol I 转录位点的 R 环和 DNA 损伤积累，也会导致基因表达的改变。因此，我们证明了在 RNA Pol II 转录过程中，两种核 T. brucei RNase H 酶的功能分离，但在宿主免疫逃避过程中，RNA Pol I 介导的基因表达过程中存在功能重叠。
