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  • 信使 RNA - 高级

    Lariat structure

    Why a lasso?
    ::为什么是套索?

    A lariat can refer to a rope in the form of a lasso. But it is also a genetic structure involved in splicing .
    ::拉里雅特可以指以拉索为形式的绳索,但它也是一个与串联有关的基因结构。

    Eukaryotic mRNA Processing
    ::Eukarytocy mRNA 处理器

    Following an mRNA is produced. However, newly transcribed eukaryotic mRNA is not ready for . This mRNA requires extensive processing, and so is known as pre-mRNA . The modification processes include splicing, the addition of a 5’ cap, editing , and polyadenylation . Once these process have occurred, the mature mRNA can be exported through the nuclear pore to the cytoplasm .
    ::在生产 mRNA 之后, 生产了 mRNA 。 但是, 新转录的 eukarycoy mRNA 还没有准备好 。 这个 mRNA 需要大量处理, 也被称为 pret- mRNA 。 修改过程包括拼写、 添加一个 5 的上限、 编辑和多环。 一旦这些过程发生, 成熟的 mRNA 可以通过核孔出口到细胞托盘。

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    Splicing
    ::拼贴

    Humans have approximately 22,000 genes , yet make many more . How? A process called alternative splicing allows one mRNA to produce many polypeptides . To understand this concept, the structure of the pre-mRNA must be discussed.
    ::人类大约有22,000个基因,但能创造更多的基因。如何?一个被称为替代的切除过程能让一个 mRNA 生产许多多聚苯醚。为了理解这个概念,必须讨论MRNA预产期的结构。

    Eukaryotic pre-mRNA contains introns and exons . An exon is the region of a gene that contains the code for producing a protein. Most genes contain many exons, with each exon containing the information for a specific portion of a complete protein. In many , a gene's exons are separated by long regions of that have no identified function. These long regions are introns , and must be removed prior to translation. Splicing is the process by which introns are removed ( Figure ). Sometimes a process called alternative splicing allows pre-mRNA messages to be spliced in several different configurations, allowing a single gene to encode multiple proteins. Splicing is usually performed by an RNA-protein complex called the spliceosome , but some molecules have their own catalytic activity and are capable of acting like to catalyze their own splicing. Bacterial mRNAs do not have introns.
    ::Eukary pre- mRNA 包含数子和外子。 Exon 是一个包含蛋白质生产代码的基因区域。 多数基因包含许多异种, 每一个异种包含完整蛋白某一特定部分的信息。 在许多 中, 基因的异种是由没有识别功能的长区域分隔的。 这些长区域是 数子, 必须在翻译前 去除。 相混合是移数子的过程( 图表 ) 。 有时, 一个名为替代拼接的过程允许以几种不同的配置来拼接前 mRNA 信息, 允许单个基因编码多个蛋白质。 拼凑通常由叫作螺旋体的 RNA- protein 复合体进行, 但有些分子有其自身的催化作用, 并且能够像催化它们自己的螺旋。 细菌 mRNA 并不具有内子 。

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    Splicing. Splicing removes introns from mRNA. UTR is an untranslated region of the mRNA. Ribonucleoproteins are nucleoproteins that contains RNA. Small nuclear ribonuclearproteins are involved in pre-mRNA splicing.

    Exon Skipping
    ::ex 跳过

    One example of alternative splicing is with exon skipping. The D. melanogaster ( fruit fly) doublesex (dsx) gene is involved in the fly's determination system. Pre-mRNAs from this gene contain 6 eons, numbered 1-6. In males, exons 1,2,3,5,and 6 are spliced together to form the mRNA, which encodes a transcriptional regulatory protein required for male . In females, exons 1, 2, 3, and 4 are joined, and a polyadenylation signal in exon 4 causes cleavage of the mRNA at that point. The resulting mRNA is a transcriptional regulatory protein required for female development.
    ::替代复制的一个例子是外向跳转。D. melanogaster(果蝇)双性(dsx)基因参与了苍蝇的确定系统,该基因的预基因包含6 个子,编号为 1-6。在雄性中,1,2,3,5,6 和6被混合成 mRNA,它编码了雄性需要的笔录调节蛋白。在雌性中,1,2,3,4 和4被结合,4 的单体细胞信号导致当时的 mRNA裂痕。由此形成的 mRNA是女性发育所需的转录调节蛋白质。

    Lariat Structures
    ::Lariat 结构

    Spliceosomal splicing and self-splicing involves a two-step biochemical process. Both steps involve reactions that occur between RNA nucleotides . First, the 2'-OH of a exon-intron junction nucleotide within the intron binds to the first nucleotide of the intron at the 5' splice site, forming an intermediate known as a lariat . Second, the 3'-OH of the released 5' exon then binds to the last nucleotide of the intron at the 3' splice site thus joining the exons and releasing the intron lariat.
    ::相形相形相形和自相残杀涉及两步生化过程,两步步骤都涉及RNA核糖核酸之间发生的反应。第一,内子内前天枢纽核酸的2'OH与5号断层点的异质原子第一个核酸结合,形成一个被称为拉里雅特的中间体。第二,释放的5号前方的3'OH,然后与3号断层点的异质最后核酸结合,从而加入异质并释放异质。

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    The two-step chemistry of mRNA splicing.

    5' cap Addition
    ::5“上限5”上限

    How does the mRNA know it is time to leave the ? Once the mRNA leaves the nucleus, how does it find a ? A signal on the front, 5’-end of the mRNA helps with both jobs. This signal is the 5’ cap . The 5' cap is a modified guanine nucleotide ( a 7-methylguanosine) added to the 5’-end of the pre-mRNA soon after the start of transcription. This 5’ cap is crucial for recognition and proper attachment of the mRNA to the ribosome, as well as protection from exonucleases, enzymes that degrade . Specifically the 5' cap adds stability from RNases. The process of 5' capping is vital to creating mature messenger RNA prior to translation.
    ::MRNA如何知道现在该离开?当MRNA离开核时,它如何找到一个信号?在前端,MRNA的5个端对这两种工作都有帮助。这个信号是5的上限。5的上限是经过修改的guanine nucleotide(一种7-甲基guanosine),这是在转录开始后不久MRNA前5端添加的。这5的上限对于MRNA的识别和适当附着到肋骨以及防止排出物、降解的酶的防护至关重要。具体地说,5的上限增加了RNases的稳定性。 5的上限过程对于在翻译之前创建成熟的送信员RNA至关重要。

    The cap is also known as a 7-methylguanosine cap, abbreviated m 7 G.
    ::上限也称为7甲基guanosine上限,缩写 m7G。

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    5' (7-methylguanosine) cap structure.

    Editing
    ::编辑编辑

    In certain instances, the nucleotide sequence of an mRNA will be changed to allow the mRNA to produce multiple proteins. This process is called editing . The classic example is editing of the apolipoprotein B (APOB) mRNA in humans. APOB is a protein that is responsible for carrying cholesterol to tissues . It is the primary lipoprotein of LDL (low density lipoprotein).
    ::在某些情况下, mRNA 的核糖核酸序列将被修改, 以便允许 mRNA 生产多种蛋白质。 这个过程被称为编辑。 典型的例子就是编辑人类体内的 polipopotatein B( APOB) mRNA。 APOB 是一种蛋白质, 将胆固醇携带到组织中。 这是LDL( 低密度脂蛋白) 的主要脂质。

    The APOB protein occurs in the plasma in two main forms, APOB48 and APOB100. APOB48 has 48% of the molecular weight has APOB100. The first is synthesized exclusively by the , the second by the liver . Both proteins are coded for by the same gene, which is transcribed into a single pre-mRNA. Editing changes a C to a U in the mRNA, changing a CAA codon (Glutamine) to a UAA codon, which is a premature (early) stop codon . Hence, upon translation this base change results in a smaller protein. As a result of the RNA editing, APOB48 and APOB100 share a common N-terminal sequence, but APOB48 lacks APOB100's C-terminal region. APOB48 contains only the first 2152 amino acids of the full-length 4536 amino acid APOB100.
    ::PAPOB蛋白以两种主要形式出现在等离子体中:APOB48和APOB100。APOB48拥有48%的分子重量是APOB100。第一种是完全由......,第二种是肝脏合成的。两种蛋白都是用同一基因编码的,转录成单一的MRNA前基因。在 mRNA中将C改成UU,将CAA Codon(Glutamine)改成UAAA Codon(早期)停止的codon。因此,在将这一基数变化转换成一个较小的蛋白质时,PAPOB48和APOB100采用相同的N终点序列,但APOB48没有APOB100的C终点区域。APOB48只含有第1,152个全长4536氨酸APOB100的氨酸。

    Polyadenylation
    ::聚合

    In eukaryotic cells , the transcription of the polyadenylation signals indicates the termination of the process. The mRNA transcript is then cut off of the RNA polymerase and freed from the DNA. The cleavage site is characterized by the presence of the sequence AAUAAA near the end of the transcribed message. Polyadenylation then occurs. Polyadenylation is the addition of a poly(A) tail to the 3’-end of the mRNA. The poly(A) tail may consist of as many as 80 to 250 adenosine residues. The poly(A) tail protects the mRNA from degradation by exonucleases. Poladenylation is also important for transcription termination, export of the mRNA from the nucleus, and translation.
    ::在光学细胞中,多词性信号的转录表明该过程的结束。 mRNA 记录稿随后从RNA聚合酶中分离出来,从DNA中解脱出来。裂痕点的特点是在转录电文末尾附近有AAUAAAA的序列。然后发生多词性反应。聚合式反应是将聚(A)尾巴添加到 mRNA的3端。聚(A)尾巴可能由多达80至250 adenosine残留物组成。聚(A)尾巴保护 mRNA不因解脱而退化。对转录终止、将 mRNA从核中输出和翻译也很重要。

    Summary
    ::摘要

    • Newly transcribed eukaryotic mRNA is not ready for translation; this mRNA requires extensive processing, including splicing and polyadenylation.
      ::新近转录的电子曲解 eukarycoy mRNA 尚未准备就绪,无法翻译;这种mRNA 需要大量处理,包括拼写和多词拼写。

    Review
    ::回顾

    1. What is pre-mRNA?
      ::什么是MRNA预产期?
    2. Define introns and exons.
      ::定义电流和电流。
    3. Describe processes of RNA modification before it leaves the nucleus.
      ::描述RNA在离开核心之前的修改过程。
    4. Describe the lariat structure process.
      ::描述拉里雅特结构过程。
    5. Define alternative splicing. Why do you think it is important?
      ::定义替代组合。 为什么你认为这很重要?