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    Home > Biochemistry News > Biotechnology News > Chinese scholar Science's latest article: unique double-stranded RNA synthesis mechanism

    Chinese scholar Science's latest article: unique double-stranded RNA synthesis mechanism

    • Last Update: 2022-01-10
    • Source: Internet
    • Author: User
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    Transposon (transposon) was first discovered in corn by American geneticist Barbara McClintock, and it is widely distributed in the genomes of bacteria, viruses, and eukaryotes
    .
    Transposons are similar to endogenous viruses and can "copy and paste" their own DNA in the host genome to achieve the purpose of self-reproduction

    .
    Active transposon poses a serious threat to the stability of the genome.
    Higher organisms maintain the stability of the genome by silencing the transposon DNA by methylation modification

    .

    The RNA-guided DNA methylation (RdDM) pathway is an important pathway for the methylation of the genome of higher plants
    .
    In this pathway, two RNA polymerases unique to plants (Pol IV and Pol V) play a central role

    .
    Pol IV cooperates with RDR2 to produce small interfering RNA dsRNA precursors, which are processed to form 24-base small interfering RNAs, and then these small interfering RNAs are paired with scaffold RNA produced by RNA polymerase Pol V with the help of Argonaut protein.
    Thereby recruiting DNA methyltransferase (DRM2) to complete the methylation of DNA

    .

    Pol IV and Pol V are the fourth and fifth multi-subunit RNA polymerases of eukaryotes.
    Their gene transcription regions, transcription initiation, extension and termination mechanisms, and transcription regulation methods are all compatible with Pol I, Pol II and Pol.
    III has a big difference

    .
    The unique feature of Pol IV transcription is that Pol IV can form a complex with RDR2 and directly catalyze the synthesis of dsRNA using double-stranded genomic DNA as a template

    .
    Although the plant Pol IV and Pol V was discovered in 2005, but its three-dimensional structure has still not been reported, affecting a further study on Pol IV and Pol V's

    .

    Recently, Zhang Yu's research team, Wang Jiawei's research team, and Zhejiang University Feng Yu's team from the Center for Excellence in Molecular Plant Science of the Chinese Academy of Sciences have worked together to analyze the structure of plant Pol IV for the first time, revealing the assembly of two RNA polymerases of plant Pol IV-RDR2 Unique complex structure, and proposes that Pol IV-RDR2 uses the internal transfer mechanism of the substrate to realize the synthesis of double-stranded RNA using double-stranded DNA as a template
    .

    This research overcomes the bottleneck of the preparation of low-abundance super-large protein complexes.
    The endogenous Pol IV-RDR2 complex was purified through the suspension cell system of Arabidopsis thaliana, and then the Pol IV-RDR2 complex was analyzed by cryo-electron microscopy single particle reconstruction technology.
    The cryo-EM structure of RDR2 holoenzyme and Pol IV-RDR2 transcription extension complex, combined with biochemical and genetic experiments, further clarified the molecular mechanism of Pol IV and RDR2 cooperation

    .

    Studies have found that the three-dimensional structure supports the evolution of Pol IV from Pol II.
    However, hundreds of millions of years of evolution have made the catalytic center and external structural units of Pol IV different from Pol II

    .
    First, the external structural unit of Pol IV protein cannot interact with Pol II specific transcription initiation factors such as TFIIB, TFIIE, TFIIF, etc.
    , thereby ensuring that the transcription of Pol IV and Pol II are independent of each other

    .
    Second, changes in the core elements of the Pol IV catalytic center indicate that the Pol IV transcription process is prone to stagnation and regression

    .

    The most significant finding of this study is that Pol IV and RDR2 form a stable complex, and the catalytic centers of these two polymerases are connected by an internal channel, and the single-stranded RNA synthesized by Pol IV using double-stranded DNA as a template passes through This internal channel is directly passed to RDR2, so that RDR2 can use this single-stranded RNA as a template to output double-stranded RNA
    .
    Based on this, the researchers proposed a model in which the Pol IV-RDR2 complex uses the mechanism of internal delivery of RNA to achieve double-stranded DNA as a template to synthesize double-stranded RNA

    .
    First, Pol IV advances on the genomic DNA and uses double-stranded DNA as a template to synthesize single-stranded RNA of a certain length.
    During the transcription extension process, due to the multiple obstacles of the chromosome and the inherent nature of Pol IV, the transcription of Pol IV is suspended and regressed.
    In the process of Pol IV's regression, the single-stranded RNA synthesized by Pol IV enters the catalytic center of RDR2 from the internal channel, and the single-stranded RNA is then used as a template to synthesize double-stranded RNA by RDR2

    .
    In the process of double-stranded RNA synthesis, RDR2 will cause the single-stranded RNA synthesized by Pol IV to gradually dissociate from the catalytic center of Pol IV

    .
    Finally, RDR2 completes the synthesis and release of double-stranded RNA

    .
    The above-mentioned special mechanism of action can ensure that the single-stranded RNA synthesized by Pol IV is directly delivered to RDR2, preventing the degradation of single-stranded RNA.
    In addition, after a round of double-stranded RNA synthesis, Pol IV-RDR2 returns to the starting point of transcription and can start downloading A round of double-stranded RNA synthesis can efficiently realize the amplification of double-stranded RNA

    .

    This study revealed for the first time the three-dimensional structure of the fourth multi-subunit RNA polymerase in eukaryotes, elucidated the unique molecular mechanism of two RNA polymerases Pol IV and RDR2 cooperative transcription, and answered how double-stranded RNA is synthesized in the RdDM pathway Scientific issues
    .
    The research results expand the structure and function of eukaryotic RNA polymerase, and deepen the understanding of plant epigenetic mechanisms

    .

    The related results were titled Pol IV and RDR2: A two-RNA-polymerase machine that produces double-stranded RNA, and were published in Science on December 24
    .
    The research was funded by the National Natural Science Foundation of China, the Strategic Leading Science and Technology Project of the Chinese Academy of Sciences, the Shanghai Basic Research Special Zone Project, and the key deployment projects of the Chinese Academy of Sciences

    .


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