Name: operon control by activators and repressors
Uploaded: 2020-11-23T11:47:37.000Z
Duration: 1 min 58 s
Channel: JoVE

원핵생물은 원형 게놈을 포함하고 있으며, 많은 경우 특정 생화학적 과정에 대한 관련 유전자가 DNA 염기서열에서 서로 직접 인접해 있습니다. 
오페론(operon)으로 알려진 이러한 유전자 클러스터는 단일 프로모터를 가지며 단일 mRNA로 전사됩니다.오페론의 발현은 각각 전사를 촉진하거나 억제하는 단백질인 활성인자(activator)와 억제인자(repressor)에 의해 조절됩니다. 
활성제는 프로모터에 결합하여 RNA 중합효소의 결합과 오페론의 후속 전사를 유도합니다.
억제인자(repressor)는 오퍼레이터(operator)로 알려진 프로모터 근처에 위치한 다른 DNA 염기서열과 상호 작용합니다. 억제 인자(repressor)가 오퍼레이터(operator)에 결합하면 RNA 중합효소가 프로모터에 결합하는 것을 방지하여 전사를 억제합니다.
원핵 유전자 조절은 종종 영양소 가용성에 따라 달라집니다.일부 박테리아에서는 포도당 농도가 낮을 때 고리형 AMP가 축적됩니다. 
고리형 AMP는 활성제인 카타볼라이트 활성제 단백질에 결합하고, 함께 프로모터에 결합합니다. 이것은 박테리아가 포도당 이외의 당을 대사할 수 있도록 하는 유전자를 포함하는 오페론인 락 오페론(lac operon)의 발현을 시작합니다.
트립토판은 단백질 합성에 필요한 아미노산입니다.환경에서 사용할 수 없는 경우 일부 유기체는 자체 트립토판을 생산할 수 있습니다. 합성을 위한 유전자는 억제자에 의해 조절되는 오페론에 존재합니다.
트립토판 농도가 높으면 억제 인자와 관련이 있습니다. 그런 다음 이 복합체는 오퍼레이터에 결합하여 RNA 중합효소를 차단하고 전사를 억제할 수 있습니다.

<ol>
	<li>Alberts et al., 6판; 380-383페이지</li>
	<li>Shaw, K. (2008) 원핵 생물의 음성 전사 조절. 자연교육 1(1):122</li>
</ol>

원핵생물의 전사 활성화제 및 억제인자

Prokaryotic Transcriptional Activators and Repressors

원핵생물의 게놈 내 유전자 구성은 진핵생물의 유전자 구성과 현저히 다릅니다. 원핵생물의 유전자는 동일한 생화학적 과정이나 기능에 관여하는 단백질의 유전자가 그룹으로 함께 위치하도록 구성됩니다. 이 유전자 그룹은 조절 요소와 함께 집합적으로 오페론으로 알려져 있습니다. 오페론의 기능성 유전자는 함께 전사되어 폴리시스트론 mRNA로 알려진 단일 가닥의 mRNA를 생성합니다.

오페론에서 원핵생물 유전자의 전사는 활성화제와 억제인자로 알려진 두 가지 유형의 DNA 결합 단백질에 의해 조절됩니다. 활성화제는 전사 개시 부위인 프로모터에 결합하고 전사에 관여하는 주요 효소인 RNA 폴리머라제의 결합을 돕습니다. 억제인자는 작동자에 결합하여 프로모터와 유전자 사이의 오페론에 있는 조절 서열을 단축시키고 RNA 중합효소가 프로모터에 결합하는 것을 억제합니다.

활성화제와 프로모터의 구조적 전제조건은 이것이 두 가지 대체 형태, 즉 DNA에 결합할 수 있는 형태와 결합할 수 없는 형태로 존재할 수 있어야 한다는 것입니다. 활성화제의 또 다른 특징은 RNA 중합효소와 DNA 모두에 동시에 결합하는 두 개의 결합 표면을 가지고 있다는 것입니다. 두 분자의 이러한 동원은 중합효소를 프로모터에 더 가깝게 만들고 결합을 돕습니다. 활성화제는 전사에서 촉매 역할을 하지 않으며 그 기능은 효소와 DNA의 결합을 촉진하는 것으로 제한됩니다. 활성화제가 없는 경우에도 RNA 중합효소는 여전히 DNA에 결합하여 낮은 수준의 발현을 보일 수 있습니다. 이 시스템에 억제인자가 존재하면 해당 유전자의 기본 발현이 방지됩니다.

원핵생물 유전자의 발현 조절은 유기체의 영양소 가용성 및 요구사항에 크게 좌우됩니다. 이러한 영양소는 오페론에 대한 활성화제 인자와 억제인자의 결합을 제어하고 필요한 유전자 세트만 발현되도록 보장합니다. 예를 들어, 세포에 트립토판이 존재하면 trp 오페론의 전사와 그에 따른 트립토판 생산을 방지하는 억제인자에 결합하게 됩니다.

게놈에서 원핵 유전자의 조직은 진핵 생물의 조직과 현저하게 다릅니다. 원핵 유전자는 유전자가 조직되어 있습니다.

prokaryotic-transcriptional-activators-and-repressors

Education

교육

JoVE Core

Molecular Biology

분자생물학

Unit 1

제1단원

Gene Expression

유전자 발현

KEY TERMS AND CONCEPTS

주요 용어 및 개념

operon control by activators and repressors

Operon control in prokaryotes depends on activators and repressors. Prokaryotic genes are often arranged in groups, not one by one like in eukaryotes. Genes that help carry out the same biochemical process are placed together with their regulatory elements. This group is called an operon, and it is transcribed into a single polycistronic mRNA strand.

Activators and repressors are DNA-binding proteins that control transcription in an operon. Activators bind near the promoter, which is the site where transcription begins. They help RNA polymerase, the enzyme that makes RNA, bind to the promoter. Repressors bind to operators, short regulatory sequences between the promoter and the genes, and they block RNA polymerase from binding to the promoter.

These proteins must switch between two shapes. One shape allows them to bind DNA, and the other does not. Activators also have two binding surfaces. One surface binds DNA, and the other binds RNA polymerase at the same time. This brings the polymerase closer to the promoter and helps transcription start. Activators do not catalyze transcription. Their role is to help the enzyme and DNA come together.

Without an activator, RNA polymerase can still bind to DNA, but only at low levels. If a repressor is present, even this basal expression is prevented. In prokaryotes, gene expression is largely controlled by nutrient availability and the needs of the cell. These nutrients affect whether activators and repressors bind to the operon, so only the needed genes are expressed. For example, when tryptophan is present in a cell, it binds to a repressor and stops transcription of the trp operon. This also prevents more tryptophan from being made.

Operon Control by Activators and Repressors

operon-control-by-activators-and-repressors

cell specific gene expression

How Cells Switch Genes On and Off

Cells switch genes on and off to make different proteins for different jobs. In multicellular organisms, many cell types are built from the same DNA, but they do not use the same genes in the same way. This difference in gene expression helps explain why cells can look and act so differently. Liver cells are a clear example. They help detoxify blood, make bile to help digest fats, and produce proteins needed for metabolism. To do these jobs, liver cells must express a specific set of genes.

regulation of expression occurs at multiple steps

regulation-of-expression-occurs-at-multiple-steps

How Cells Control Gene Expression

Cells control gene expression at several points between DNA and protein. The most common control point is transcription. At this stage, proteins bind to short regulatory DNA sequences and can either increase or reduce transcription of the linked gene. After transcription, a precursor mRNA is made. This pre-mRNA contains exons, which code for protein, and introns, which do not. It must be processed before translation, and splicing removes the introns and joins the exons. Cells can also regulate...

cis-regulatory sequences

How Cis-Regulatory DNA Controls Transcription

Cis-regulatory sequences are short, non-coding DNA segments that control gene transcription. They sit on the same chromosome as the genes they regulate and act as binding sites for transcriptional regulators. In eukaryotes, these proteins help control gene expression patterns in different cell types. These DNA sequences can be close to a gene or thousands of bases away. When they are far from the gene in the DNA sequence, they are often brought close together in space because chromosomes are...

cooperative binding of transcription regulators

cooperative-binding-of-transcription-regulators

How Transcription Factors Bind DNA

Transcriptional regulators bind to cis-regulatory DNA sequences to control gene transcription. These DNA sequences are very short, usually fewer than ten nucleotide pairs long. Because they are so short, the same sequence can appear by chance in many places across the genome. Some regulators can also bind to groups of similar sequences. That raises the chance of random binding even more. To lower this risk, transcription regulators often form dimers, which are pairs of proteins that bind a DNA...

prokaryotic transcriptional activators and repressors

Operon control in prokaryotes depends on activators and repressors. Prokaryotic genes are often arranged in groups, not one by one like in eukaryotes. Genes that help carry out the same biochemical process are placed together with their regulatory elements. This group is called an operon, and it is transcribed into a single polycistronic mRNA strand. Activators and repressors are DNA-binding proteins that control transcription in an operon. Activators bind near the promoter, which is the site...

operons

Operons in Bacterial Gene Control

Operons help bacteria control groups of genes at the same time. An operon is a set of genes that are regulated together and can be turned on or off as a unit. This shared control helps bacteria respond quickly to changes in their environment. In many operons, a promoter gives RNA polymerase a place to bind and start transcription. The operon also includes a regulatory region that helps control whether the genes are expressed. When conditions change, the cell can use this setup to manage gene...

the eukaryotic promoter region

Eukaryotic Promoter Motifs and Gene Control

The eukaryotic promoter region is a stretch of DNA located upstream of a gene. It includes an RNA polymerase binding site, a transcription start site, and several cis-regulatory sequences. These DNA signals help control when transcription begins. The promoter can be divided into proximal and distal regions. The proximal promoter lies close to the gene and includes cis-regulatory sequences and the core promoter. The core promoter is the RNA polymerase binding site, and it is usually found...

co-activators and co-repressors

Chromatin Control in Gene Transcription

Chromatin control plays a major role in gene transcription in eukaryotes. Gene expression is regulated by several proteins that work together at a gene regulatory site. Some of these proteins bind directly to specific DNA sequences, while co-regulators attach to those regulators but do not bind DNA on their own. Co-regulators can act as co-activators or co-repressors, depending on the complex they join. One co-regulator may even switch roles in different settings. For example, the...

eukaryotic transcription activators

How Transcription Activators Turn Genes On

Transcription activators are proteins that help turn genes on by promoting transcription from DNA to RNA. They often have two parts. One part binds to DNA, and the other part activates transcription. In some proteins, such as the glucocorticoid receptor and MyoD, one domain can do both jobs. The DNA-binding part recognizes specific regulatory sequences on the DNA. These binding domains are grouped into families based on their structure. Common examples include the leucine zipper, zinc finger,...

eukaryotic transcription inhibitors

How Eukaryotic Gene Repressors Work

Eukaryotic gene repressors help turn specific genes off when the cell needs to control growth, development, or other biochemical processes. These DNA-binding proteins regulate gene expression in eukaryotes. Their presence at the right time and place can be triggered by hormones and signals from other cells. Most transcription inhibitors have two main parts. One part binds DNA, and the other is a repressor domain, which helps shut down transcription. Repressor domains can connect with basal...

combinatorial gene control

Gene Expression by Transcription Factor Combinations

Gene expression can depend on combinations of transcription factors working together. In combinatorial gene control, several transcription factors act in a coordinated way to regulate a single gene. If one or more of these factors are missing, the level of gene expression or repression can change a lot. This kind of control helps explain how a relatively small number of transcription factors can regulate a very large number of genes. More than 30,000 genes are controlled by about 2,000 to...

induced pluripotent stem cells

Reprogramming Cells into Stem Cells

Induced pluripotent stem cells are created by reprogramming mature cells back into a stem-cell state. This process shows that specialized cells can be changed into cells with broader developmental potential. The topic is important in biology because it links cell identity, gene control, and stem cell research. These cells begin as ordinary body cells and are pushed to de-differentiate, or lose their specialized features. After reprogramming, they behave like pluripotent stem cells, which means...

master transcription regulators

MEF2C and Gene Control Cascades

MEF2C is a master transcription regulator that controls gene expression in coordinated cascades. These regulators are proteins that manage the activity of multiple genes that often work together to produce a complex outcome. When a master transcription regulator is activated, it can start a chain of transcriptional activation that supports that outcome. Master transcription regulators can act in two main ways. They may bind directly to the regulatory sequences of several genes involved in a...

epigenetic regulation

DNA Methylation and Histone Changes

Epigenetic regulation controls gene activity without changing the DNA sequence. It helps determine when genes are turned on or off in a cell. Two major epigenetic mechanisms are DNA methylation and histone modification. DNA methylation adds chemical groups to DNA, while histone changes affect how tightly DNA is packed around histone proteins. These changes can make genes easier or harder to use. In high school biology, epigenetic regulation is important for understanding how cells with the...

genomic imprinting and inheritance

Genomic Imprinting in Human Disease

Genomic imprinting affects how some inherited genes are turned on or off in human cells. Diploid organisms inherit chromosomes from both parents, and each gene usually has two alleles. In most cases, both alleles are expressed. If one allele is missing or mutated, the other can often compensate, but some genes do not work that way. In genomic imprinting, a gene or its regulatory sequence carries chemical tags, such as methyl groups, on the copy inherited from only one parent. These tags are...

key terms and concepts

Learn how activators and repressors control prokaryotic operons, from promoter binding to the trp operon response to tryptophan in cells.

Operon Control by Activators and Repressors | JoVE K12

molecular biology

JoVE Core 분자생물학은 명확하고 간결한 애니메이션을 통해 분자 단계에서 일어나는 세포 과정을 설명합니다.또한, 과학자가 직접 실험을 진행하는 실사 영상을 통해 분자생물학 개념의 응용 사례를 보여줍니다.

Operon Control by Activators and Repressors

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