细菌中RNase HI介导RNA降解的研究进展

Research progress in RNase HI-mediated RNA degradation in bacteria

摘要:

在细菌细胞中，为了维持基因组稳定和正常的生命活动，RNase HI通常以降解RNA/DNA杂合链中RNA的方式来防止复制中引物的积累以及转录中R环的形成。RNase HI对底物的识别主要依赖于DNA与RNA结合槽，对底物的催化主要依赖于DEDD基序和位于活性位点附近柔性环中的一个组氨酸。以Mg²⁺为代表的金属离子在催化过程中发挥了至关重要的作用。杂交双链中ssDNA突出部分的类型决定了RNase HI的作用模式：在没有突出或在ssDNA的5′端存在突出部分的情况下，RNase HI作为一种非序列特异性核酸内切酶随机地降解RNA；当ssDNA的3′端存在突出部分时，RNase HI依靠5′核酸外切酶活性对RNA进行连续切割。RNase HI、Rep、DinG和UvrD通过与单链DNA结合蛋白(single-stranded DNA-binding protein, SSB)的C端尾部的6个残基相互作用被招募到复制叉附近，并可能以协作的方式解决复制-转录冲突。RNase HI的缺失或活性降低将引起DNA结构不稳定、基因突变、转录装置回溯和复制不协调等一系列有害后果。RNase HI在反义技术、R环检测和联合抗生素的靶向治疗等方面展现出巨大的应用价值。关于RNase HI与其他酶降解引物的合作机制也是未来值得研究的一个内容。

Abstract:

In bacterial cells, RNase HI usually degrades RNA in the RNA/DNA hybrids to prevent the accumulation of primers in replication and the formation of R-loops in transcription, thus maintaining genomic stability and normal life activities. The recognition of substrates by RNase HI mainly depends on DNA- and RNA-binding grooves, and the catalysis of substrates by RNase HI mainly depends on the DEDD motif and a histidine located in a flexible loop near the active site. Metal ions represented by Mg²⁺ play an important role in the catalytic process. The mode of action of RNase HI is determined by the type of ssDNA overhangs on RNA/DNA hybrids. In the presence of a 5' ssDNA overhang or in the absence of any overhang on RNA/DNA hybrids, RNase HI functions as a non-sequence-specific endonuclease to degrade RNA randomly. In the presence of a 3' ssDNA overhang on RNA/DNA hybrids, RNase HI relies on 5'-exonuclease activity for the successive degradation of RNA. RNase HI, Rep, DinG, and UvrD are recruited near the replication forks by interacting with the six residues of the C-terminal tail of single-stranded DNA-binding protein (SSB), and may resolve replication-transcription conflicts in a cooperative manner. The deletion of RNase HI or the decrease in RNase HI activity will cause a series of harmful events such as DNA structural instability, gene mutation, transcriptional machinery backtracking, and replication incoordination. RNase HI has shown great application prospects in antisense technology, R-loop detection, and targeted therapy combined with antibiotics. The cooperative mechanism of primer degradation by RNase HI and other enzymes is also worth studying in the future.