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  • 基因表达式的推进调节 - 高级

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    On or off?
    ::开还是关?

    When it comes to genes , that is an important question. And if you're a single-celled organism like a , conserving energy by not producing unnecessary is very important. So if a protein is not needed, that bacterium wants to keep those genes off.
    ::当涉及到基因时,这是一个重要问题。如果你是一个单细胞生物体,就像一个单一细胞生物,那么通过不生产不必要的物质来节能是非常重要的。因此,如果不需要蛋白质,细菌就想保持这些基因的关闭。

    Prokaryotic Gene Regulation
    ::蛋白质基因规范

    In , a combination of activators and repressors determines whether a gene is transcribed. As you know, prokaryotic organisms are fairly simple organisms with much less . Prokaryotic genes are arranged in operons , a region of DNA with a promoter , an operator , and one or more genes that encode proteins needed to perform a certain task. To maintain (and survive), the organism must quickly adapt changing environmental conditions. The regulation of plays a key role in this process.
    ::在其中,由活性者和抑制者共同决定基因是否被转录。如你所知,蛋白质有机体是相当简单的有机体,远远不那么简单。 蛋白质基因安排在线条中,一个DNA区域,有一个提倡者、一个操作者,以及一个或一个以上基因,将履行某种任务所需的蛋白质编码。为了保持(和生存),有机体必须迅速适应不断变化的环境条件。在这一过程中,调节作用至关重要。

    For a bacteria, many aspects of gene regulation are due to the presence or absence of certain nutrients . In prokaryotes, repressors bind to regions called operators that are generally located immediately downstream from the promoter. Activators bind to the upstream portion of the promoter.
    ::对于细菌来说,基因监管的许多方面是由于某些营养物的存在或缺乏。 在prokaryotes,抑制剂与通常位于推广者下游的称为“操作者”的地区捆绑在一起。 活性剂与推广者的上游部分联系在一起。

    The Lac Operon
    ::拉克·奥佩伦

    The lac operon ( Figure ) is an operon required for the transport and metabolism of lactose in E. coli . The lac operon is regulated by the availability of lactose. The lac operon consists of a promoter, an operator, three adjacent structural genes which code for and a terminator. The three genes are: lacZ, lacY, and lacA. The Z gene encodes β-galactosidase, the Y gene encodes permease, and the A gene encodes transacetylase. All three genes are controlled by the same regulatory elements . 
    ::lac operon (Figure ) 是 E. coli 中乳糖迁移和新陈代谢所需的一种活性。 lac operon 受乳糖的可用性制约。 lac operon 由促进者、 操作者、 三个相邻的结构基因组成, 编码和终止者。 三种基因是: lacZ、 lacY 和 lacA。 Z 基因编码为 β- galactosidase 、 Y 基因编码为 permese 和 A 基因编码为 tranacetylase 。 所有三种基因都由相同的管理要素控制 。

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    The lac operon. The lac operon contains genes for three enzymes, lac, lacY, and lac A, as well as the promoter, operator, and terminatory regulatory regions.
    ::Lac 操作程序。 Lac 操作程序包含三个酶的基因, 包括 lac, lac, lacY, lac A, 以及促进者, 操作者, 和终止控制区的基因。

    In bacteria, the lac repressor protein blocks the synthesis of enzymes that digest lactose when there is no lactose present. When lactose is present, it binds to the repressor, causing it to detach from the DNA strand. This mechanism is known as induction and is illustrated in Figure .
    ::在细菌中,压压器蛋白将吸收乳糖的酶合成成块,当没有乳糖存在时消化乳糖。当乳糖存在时,它与压压压器绑在一起,导致它从DNA链中分离出来。这个机制被称为诱导,并在图中加以说明。

    Specific control of the lac operon depends on the availability of lactose. The enzymes needed to metabolize lactose are not produced when lactose is not present. When lactose is available, and therefore needs to be metabolized, the operon is turned on, RNA polymerase binds to the promoter, and the three genes are transcribed into a single mRNA molecule. However, if lactose is not present (and therefore does not need to be metabolized), the operon is turned off by the lac repressor protein.
    ::lac Operon 的具体控制取决于乳糖的供应情况。 乳糖不存在时, 不需要产生新陈代谢乳糖所需的酶。 当乳糖存在时, 并且因此需要代谢, 就会打开阴极, RNA 聚合酶与促销者捆绑在一起, 三个基因被转录成单一的 mRNA 分子。 但是, 如果乳糖不存在( 因此不需要代谢) , 阳极则由 lac 抑制蛋白关闭 。

    The lacI gene, which encodes the lac repressor, lies near the lac operon and is constitutively expressed. Therefore, the lac repressor protein is always present in the bacteria. In the absence of lactose, the lac repressor protein will bind to the operator, just past the promoter in the lac operon. The repressor blocks the binding of RNA polymerase to the promoter, keeping the operon turned off. Under this condition, no mRNA is produced from the operon.
    ::将压压器编码的 lacI 基因, 位于 Lac 操作器附近, 并具有组织性表达。 因此, lac 压压器蛋白总是存在于细菌中 。 如果没有乳糖, lac 抑制器蛋白就会与操作者结合, 刚过 Lac 操作器的促销者 。 压压器将 RNA 聚合酶的粘合物与促进者隔开, 保持操作器的关闭 。 在此条件下, 没有从操作器中产生 mRNA 。

    When lactose is available, a lactose metabolite called allolactose binds to the allosteric site on the repressor.. This interaction causes a conformational change in the repressor shape and the repressor falls off the operator, allowing RNA polymerase to bind to the promoter and initiate transcription. Allolactose is called an inducer because it turns on, or induces the expression of the lac genes.
    ::当有乳糖时,一种叫做 Alolactose 的乳糖代谢物会与压压器上的 Alostasteric 站点结合。 这种相互作用导致压压压器形状的整齐变化,压压压器从操作器上掉下来,使RNA聚合酶与促销器捆绑并开始转录。 ALactose 被称为诱导器, 因为它打开, 或者诱导拉克基因的表达。

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    Regulation of the lac operon. When lactose is present, RNA polymerase (red) binds to the promoter (P) and the three genes are expressed, producing a single mRNA for the three genes. When lactose is unavailable, the lac repressor (yellow) binds to the operator (O) and inhibits the binding of RNA polymerase to the promoter. The three genes are not expressed. For an animation of the Lac Operon, see .
    ::当乳糖存在时,RNA聚合酶(红色)与促销者(P)结合,三种基因表示,为三种基因产生单一的mRNA。当乳糖不存在时,lac抑制器(黄色)与操作者(O)结合,禁止RNA聚合酶与促销者结合。三种基因没有表示。Lac Operon的动画见。

    The Trp Operon
    ::Trp 欧佩伦

    The trp operon , shown in Figure  is an operon that codes for the components for production of the amino acid tryptophan. This operon is regulated so that it is not utilized in the presence of tryptophan. This is an example of negative regulation of , with tryptophan inhibiting this operon.
    ::图中显示的trp operon, 是用于生产氨基酸的成分的代码的线条。 该线条受管制, 以免在有trptophan 的情况下使用。 这是对trptophan 进行负面监管的一个例子, 使用trptophan 来抑制这个线条 。

    This operon contains five structural genes: trpE, trpD, trpC, trpB, and trpA, which encode tryptophan synthetase, an enzyme that catalyzes the final two steps in the biosynthesis of tryptophan. The operon also contains a promoter which binds to RNA polymerase and an operator sequence, as well as a constitutively expressed repressor gene (trpR) located upstream from the structural genes and their promoter. The repressor gene synthesizes a repressor protein that can bind to the operator sequence.
    ::该阳极含有五种结构基因:trpE、trpD、trpC、trpB和trpA,它们编码了trpppphan合成酶,这是一种酶,催化了trptophan生物合成的最后两步。该阳极还含有一种与RNA聚合酶和操作序列相连的促销器,以及一种结构基因及其促销器上方的有机表达的抑制基因(trpR)。抑制器基因合成了一种能与操作器序列结合的抑制剂蛋白。

    In the absence of tryptophan, the trp operon is active. In the presence of tryptophan, the operon is inactive. When tryptophan is present, the repressor protein and tryptophan bind together, causing a conformational change in the repressor, allowing it to bind to the operator. When the repressor protein is bound to the operator, transcription of the trp genes is blocked. In the lac operon, allolactose binds to the repressor protein preventing binding to the operator and allowing gene transcription, while in the trp operon, tryptophan binds to the repressor protein making it bind to the operator, effectively blocking gene transcription. In both situations, repression is that of RNA polymerase transcribing the genes in the operon. The trp operon contains a 140bp leader sequence (trpL) and an attenuator sequence between the leader and the first structural gene (trp E), which allows for graded regulation. Attenuation is an additional mechanism of negative feedback in the trp operon.
    ::在没有treptophan的情况下, trp pop operon是活跃的。 在有treptophan的情况下, operon 是不活跃的 。 当treptophan 出现时, proptophan 和 troptophen 结合了抑制器和treptophen , 导致抑制器的整形变化, 使抑制器能与操作器捆绑在一起, 从而将抑制器和treptophen 捆绑在一起, 从而将抑制器和treptophen 捆绑在一起, 从而将抑制器与操作器捆绑在一起, 从而将抑制器与操作器捆绑在一起。 当抑制器被绑在操作器中时, 将trpop gent 的基因绑在一起时, trepeoperon (trpL) 和 attenator 序列中, 领导器与第一个结构基因( trp E) 之间, 允许分级调 。 。 的减 。 在 trantation 中, 额外机制是 Treppoperon 中, 的反反反馈机制 。

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    Structure of the trp operon. The trp operon is composed of 5 structural genes, 1 regulatory gene and other regulatory sequences, including the promoter, operator and leader sequence. Within the leader sequence is the attenuator region. In the presence of tryptophan, the structural genes are not transcribed.
    ::trp operon 由 5 个结构基因、 1 个管理基因 和其他 管理 序列 组成, 包括 推动者 、 操作者和 领导者 序列 。 在 领先 序列 中 , 是 缓冲 区域 。 在 有 treptophan 的情况下 , 结构 基因 不被 转录 。

    Attenuation
    ::衰减

    Attenuation is an additional mechanism to decrease transcription of the trp operon. Attenuation is possible because the genetic material of prokaryotes in in the cell's cytoplasm with its . In prokaryotes, it is possible for ribosomes to begin translating the mRNA while RNA polymerase is still transcribing the DNA sequence, allowing to have an effect on transcription.
    ::衰减是减少trp operon转录的又一个机制。 衰减是可能的, 因为细胞细胞图层中的 prokaryotes 的遗传物质 。 在 prokaryotes 中, 肋骨可以开始翻译 mRNA, 而 RNA 聚合酶仍然在转录DNA序列, 从而能够对转录产生影响 。

    The 140bp trpL leader sequence is a section of the operon between the operator and the structural genes. This sequence is divided into four short segments designated 1-4, as illustrated in Figure . Sequence 1 is partially complementary to sequence 2, which is partially complementary to sequence 3, which is partially complementary to sequence 4, allowing the sequence to form three distinct hairpin structures identified as 1-2, 2-3 or 3-4. The hybridization of strands 1 and 2 to form the 1-2 structure prevents the formation of the 2-3 structure, while the formation of the 2-3 hairpin prevents the formation of the 3-4 structure. The 3-4 hairpin acts as a transcription termination sequence; once the 3-4 structure forms, RNA polymerase will disassociate from the DNA and transcription of the structural genes of the operon will not occur.
    ::140bptrp TrpL领导序列是操作者与结构基因之间意见书的一个部分。这一序列分为四个短段,指定为1-4,如图所示。顺序1部分补充顺序2,部分补充顺序3,部分补充顺序4,允许序列组成三个不同的发型结构,称为1-2、2-3或3-4。组成线1和2-2结构的线条1和2的混合阻止了2-3结构的形成,而2-3的发型的形成阻止了3-4结构的形成。3-4发型的3-4作为转录终止序列;3-4结构格式一旦出现,RNA聚合酶将不再与operon结构基因的DNA和转录。

    A segment of the trpL sequence codes for the leader peptide , a short polypeptide of 14 amino acids. This segment contains two adjacent tryptophan residues, which is a very rare occurrence. If the ribosome attempts to translate this leader peptide while tryptophan levels are low, translation will stall at either of the trp codons . During this time, the ribosome physically blocks segment 1 of the leader sequence, preventing it from forming the 1-2 secondary structure. Sequence 2 now forms the 2-3 structure with sequence 3, which keeps sequence 3 from forming the 3-4 structure. This 2-3 structure is called the anti-termination hairpin as it allows RNA polymerase to continue transcribing the entire operon without interference of the ribosome.
    ::顶端的顶端酸为14个氨基酸的短聚对流体。 顶端含有两个相邻的锥虫残留物, 这是非常罕见的情况。 如果在顶端酸水平低的情况下, 将头端酸翻译为顶端, 翻译将停留在trpcodon 中的任何一个端点。 在此期间, 头端序列的第 1 段的肋骨物理块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块, 防止它形成 1-2-2 2-2 3 结构组成第 3 3 序列块块块结构, 序列块块块块块块块块块块块块块块块块块块块结构结构组3 组成3 组成3 组成3 3 3 结构块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块结构结构结构结构结构结构结构结构结构结构结构结构结构结构结构结构结构结构结构。 这2-3 称为防3 根状结构块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块块

    If tryptophan levels are high, the leader peptide is translated fully and the ribosome continues through to the stop codon . The ribosome physically sits on segments 1 and 2 of the leader sequence, allowing the 3-4 hairpin structure to form, which terminates transcription as RNA polymerase falls off the DNA. The operon is only transcribed when tryptophan is unavailable for the ribosome.
    ::如果切片水平高,则先导浸泡剂会被完全翻译,而排卵剂则会一直持续到停止的阴极。 排卵剂的生理功能会坐落在第1和第2部分,让3-4个发型结构形成,它会随着RNA聚合酶从DNA中脱落而终止转录。 当排卵剂不能用于排卵剂时,排卵剂才会被转录。

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    The transcriptional attenuation of the trp operon involves the formation of mRNA stem-loops from the trpL leader region. In the presence of tryptophan the 3-4 hairpin structure acts as a termination structure, while with low levels of tryptophan the 2-3 hairpin structure allows transcription to continue. A similar attenuation mechanism regulates the synthesis of histidine, phenylalanine, and threonine.
    ::Trp Operon 的转录减速涉及从 TrpL 领头地区形成 mRNA 干螺旋体, 在有trptophan 的情况下, 3-4 个发型结构作为终止结构, 而低水平的trptophan 结构 , 2-3 个发型结构可以继续转录。 类似的减速机制管理着丁胺、苯麻拉尼和血清的合成。

      

     

    Summary
    ::摘要

    • Prokaryotic genes are arranged in operons, regions of DNA with a promoter, an operator, and one or more genes that encode proteins needed to perform a certain task.
      ::蛋白质基因安排在线条、DNA区域,有推广者、操作者、以及一种或多种基因,这些基因编码蛋白质,以完成某项任务。
    • The regulation of the lac operon is a key example of prokaryotic gene regulation. When lactose is present, RNA polymerase binds to the promoter and the operon is turned on; when lactose is unavailable, the lac repressor binds to the operator and the operon is turned off.
      ::lac operon 的调控是蛋白质基因调控的关键例子。 当乳糖存在时, RNA 聚合酶与促销者捆绑, 并打开操作器; 当没有乳糖时, lac 抑制剂与操作者捆绑, 操作器被关闭 。
    • The trp operon is an example of negative regulation.
      ::trp operon是消极管制的一个例子。
    • The trp operon is also regulated by attenuation, a process involving RNA secondary structures.
      ::trp operon还受到减速的制约,这是一个涉及RNA二级结构的过程。

    Review
    ::回顾

    1. Define an operon. Give an example.
      ::定义操作员。 请举一个例子 。
    2. Compare regulation in the lac and trp operons.
      ::比较 Lac 和 trp 线条的调控 。
    3. What is attenuation?
      ::什么是衰减?
    4. Illustrate the trp operon when tryptophan is present and absent.
      ::当triptophan存在和缺席时, 将Trp Feeron 画成图象的图例 。