Name: operons in bacterial gene control
Uploaded: 2020-11-23T11:47:37.000Z
Duration: 2 min 9 s
Channel: JoVE

- [해설자] 원핵세포 안에서 오페론은조절 요소와 몇 개의 단백질 코딩 유전자,그리고 함께 전사되는구조적 유전자를 지니고 있는유전자 서열군입니다.가장 성공한 연구 사례 중 하나는박테리아 속에 존재하는 락 오페론으로,젖당 대사에 필요한효소들을 코딩하는세 개의 유전자들인 lac-Z, lac-Y, 그리고 lac-A와락 유전자들의 발현을 조절하는프로모터, 작동자그리고 종결인자서열들을 포함합니다.일반적으로, 젖당 농도가 높을 때젖당 분해 억제 단백질은작동자에 단단히 결합하고,RNA 중합효소가 프로모터에결합하는 것을 차단함으로써락 유전자의 전사를 방지합니다.젖당 분해 억제 단백질은 구성적으로 나타나는데,이는 곧 코딩하는 유전자가기본적으로 켜저 있음을 의미합니다.포도당 농도가 매우 낮을 때,세포는 젖당을 에너지원으로 사용하게 됩니다.한번 세포 내부에 존재하게 되면,젖당의 일부는 유사 젖당체라고 불리며락 오페론의 유도제로 알려진개조된 버전의 젖당체로 바뀌게 됩니다.왜냐하면 이는 억제 인자에 결합하여락 유전자의 발현을 촉발시키기 때문입니다.또한, 낮은 수치의 포도당 레벨에서는신호 전달 물질인 사이클릭 AMP의 양이 증가하고분해 대사 활성화 단백질 (CAP)에결합하게 됩니다.이 물질들은 프로모터의 상부에 위치한조절 서열과 결합하며,RNA 중합 효소의 도움을 받아전사를 현저히 증가시키게 됩니다.전사 과정에서, mRNA 단일 가닥이 생성되며중합효소가 종결 서열에 도달하게 되면이는 방출되게 됩니다.젖당 전사 과정을 위해이 mRNA와 세 가지 단백질이 필요합니다.

Osbourn, Anne E. 및 Ben Field. "오페론." Cellular and Molecular Life Sciences 66, no. 23 (2009): 3755-3775. [<a href="https://doi.org/10.1007/s00018-009-0114-3">출처</a>]

오페론

Operons

원핵생물(prokaryote)은 오페론(operon)을 통해 유전자 발현을 조절할 수 있습니다. 오페론은 조절요소(regulatory element)와 기능적으로 관련되고 단백질 암호화(coding; 부호화; 코딩) 유전자가 밀집되어 이루어진 DNA 서열입니다. 오페론은 단일 프로모터(promoter; 촉진자) 서열을 사용해 유전자 군집(즉, 구조유전자(structural gene) 군집)을 단일 mRNA 분자로 전사(transcription)하기 시작합니다. 그리고 종결자(terminator; 종결) 서열이 전사를 마칩니다. 프로모터와 구조유전자 사이에 위치한 작동유전자(operator; 작동자) 서열은 억제인자(repressor; 억제자) 단백질로 묶인 경우 오페론의 전사 활동을 금지합니다. 전체적으로 프로모터, 작동유전자, 구조유전자, 종결자가 오페론의 핵심을 형성합니다.
 
 일반적으로 오페론은 유도하거나 억제할 수 있습니다. 박테리아 lac 오페론과 같은 유도성(inducible) 오페론은 일반적으로 “꺼져”있지만, 유도인자(inducer)라고 불리는 작은 분자가 있으면 “켜집”니다. 포도당(glucose)은 없지만 유당(lactose)이 있을 때, 유도인자인 알로락토스(allolactose)는 lac 오페론 억제인자와 결합해 억제인자를 비활성화하여, 오페론이 유당 물질대사를 담당하는 효소를 생성하도록 합니다.
 
 박테리아의 trp 오페론과 같은 억제성(repressible) 오페론은 대개 “켜져”이지만 보조억제인자(corepressor)라고 불리는 작은 분자가 있으면 “꺼집”니다. 필수 아미노산인 트립토판(tryptophan)이 풍부할 때, 트립토판은 trp 억제인자와 결합해 억제인자를 활성화하여 오페론이 합성에 필요한 효소를 만드는 것을 막습니다.
 
 오페론은 또한 지속해서 활성 상태일 수 있습니다. 예를 들어 박테리아 리보솜 RNA(ribosomal RNA, 줄여서 rRNA) 오페론은 항상 “켜진” 상태로 있습니다.
 
 다른 조절요소도 오페론의 유전자 발현에 기여합니다. 조절 유전자(regulatory gene)는 전사 활성인자(activator; 활성자) 또는 억제인자 단백질을 암호화합니다. 예를 들어, lacI와 trpR 유전자는 각각의 오페론의 억제인자를 암호화합니다. lac 오페론의 CAP(catabolite activator protein) 결합 부위와 같은 추가 조절 서열(regulatory sequence)은 다른 활성인자 또는 억제인자를 위한 결합 부위를 제공합니다. 예를 들어, 포도당이 낮으면 신호 분자(즉, cAMP)가 CAP를 활성화하여 CAP 부위에 결합하고 RNA 중합효소(RNA polymerase; RNA 폴리머레이스)를 모집하며 lac 오페론 전사를 시작합니다.

원핵생물은 오페론(조절 요소와 클러스터되고 기능적으로 관련된 DNA 염기서열)을 통해 유전자 발현을 제어할 수 있습니다.

Education

교육

JoVE Core

Molecular Biology

분자생물학

Unit 1

제1단원

Gene Expression

유전자 발현

KEY TERMS AND CONCEPTS

주요 용어 및 개념

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 activity efficiently.

Operons are a key example of gene regulation in prokaryotes. The transcript highlights the lac operon as a model for this process. Studying operons shows how bacteria coordinate gene expression without separating the genes into different control systems.

Operons in Bacterial Gene Control

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

prokaryotic-transcriptional-activators-and-repressors

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...

operons

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 operons let bacteria regulate groups of genes together, with a focus on promoters, regulatory regions, and the lac operon model.

Operons in Bacterial Gene Control | JoVE K12

molecular biology

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Operons in Bacterial Gene Control

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