Name: how eukaryotic gene repressors work
Uploaded: 2020-11-23T11:47:37.000Z
Duration: 1 min 52 s
Channel: JoVE

Los inhibidores de la transcripción son capaces de reprimir la transcripción de un gen. Tienen un dominio distinto que se une a las secuencias reguladoras del ADN y otro dominio que reprime la transcripción.
Estas proteínas pueden inhibir la transcripción a través de varios mecanismos. La más simple es bloqueando la unión de un activador a su secuencia cis-reguladora, a través de uno de varios mecanismos diferentes.
En algunos casos, el inhibidor se une competitivamente a la secuencia reguladora, evitando así la unión del activador. En otros, el inhibidor se une a un sitio cerca del sitio de unión del activador, y su dominio represor interactúa con el activador para evitar que se una a la secuencia reguladora. 
Un inhibidor también puede unirse competitivamente a los sitios de unión de factores de transcripción generales en el ADN y bloquear el ensamblaje de la maquinaria transcripcional.
Los inhibidores también pueden unirse a sus propias secuencias cis-reguladoras inhibitorias, evitando el inicio de la transcripción incluso en presencia de un activador en la región reguladora.
Uno de los mecanismos más comunes utilizados por los inhibidores de la transcripción es utilizar su dominio represor para reclutar proteínas conocidas como co-represores. Los correpresores a menudo tienen actividades enzimáticas que pueden inhibir la transcripción. 
Muchos co-represores funcionan como histonas desacetilasas, histonas metiltransferasas y otros remodeladores de cromatina. Estas modificaciones dan lugar a un empaquetamiento apretado del ADN en el nucleosoma y restringen el acceso de los factores de transcripción y la polimerasa a sus sitios reguladores, inhibiendo así la transcripción.

<ol>
	<li>Lodish H, Berk A, Zipursky SL, et al. Biología celular molecular. 4ª edición. Nueva York: W. H. Freeman; 2000. Sección 10.7, Mecanismos moleculares del control transcripcional eucariota. Disponible en: https://www.ncbi.nlm.nih.gov/books/NBK21677/</li>
	<li>Hanna-Rose, W., & Hansen, U. (1996). Mecanismos activos de represión de los represores de la transcripción eucariota. Tendencias en genética, 12(6), 229–234. doi:10.1016/0168-9525(96)10022-6</li>
	<li>Renkawitz, R. (1990). Represión transcripcional en eucariotas. Tendencias en genética, 6, 192–196. doi:10.1016/0168-9525(90)90176-7</li>
</ol>

inhibidores de la transcripción eucariotas

Eukaryotic Transcription Inhibitors

Ciertos procesos bioquímicos, como el desarrollo embrionario y la regulación del crecimiento celular, dependen de la represión de genes específicos. Las proteínas de unión al ADN conocidas como inhibidores de la transcripción eucariotas regulan la represión de la expresión genética en eucariotas. La presencia de estos inhibidores en el lugar y momento requeridos en la célula se desencadena por la presencia de hormonas y señales adicionales de otras células.

Los inhibidores de la transcripción eucariotas suelen contener dos dominios distintos, un dominio de unión al ADN y un dominio represor. Los dominios represores de los inhibidores de la transcripción pueden unirse a otras proteínas, como reguladores, activadores, coactivadores y correpresores transcripcionales basales. Los dominios de represión se pueden clasificar vagamente en función de los aminoácidos que los constituyen, como dominios ricos en alanina, dominios ricos en glutamina y dominios ricos en prolina. También se pueden categorizar como dominios ácidos o básicos, y como hidrófilos o hidrófobos. Estos dominios son a menudo intercambiables y diferentes dominios represores pueden asociarse con el mismo dominio de unión al ADN.

Los inhibidores de la transcripción eucariotas pueden llevar a cabo su función a través de tres mecanismos principales: inhibir la unión del ADN, bloquear la activación y silenciar los genes.

La inhibición de la unión al ADN evita que el activador se una al sitio promotor o potenciador, o puede evitar que el complejo de iniciación de la transcripción se una al sitio de inicio de la transcripción o a la caja TATA. Esto podría ocurrir mediante la unión del inhibidor al sitio regulador o de inicio o mediante la asociación del dominio inhibidor con activadores, coactivadores o proteínas involucradas en la maquinaria de transcripción. Por ejemplo, en humanos, el inhibidor de la transcripción NF-E se une a la caja CCAAT del gen de la γ-globina fetal e inhibe la unión del activador CP1.

El bloqueo de la activación evita que la señal de un activador de la transcripción unido a un promotor o potenciador llegue al sitio de inicio de la transcripción. Esto puede ocurrir cuando un inhibidor se une a un sitio adyacente al promotor o potenciador, como en la regulación de c-myc donde el inhibidor myc-PRF se une al lado del promotor. También puede ocurrir a través de la unión del inhibidor a un activador unido al ADN. Este tipo de represión ocurre cuando el inhibidor GAL80 en la levadura se une al activador GAL4 cuando está unido al promotor.

El silenciamiento genético ocurre cuando el inhibidor bloquea o desorganiza el complejo de inicio de la transcripción al unirse simultáneamente a una de las proteínas que constituyen la maquinaria y a un sitio del ADN cerca del sitio de inicio de la transcripción, anclando así la maquinaria de la transcripción. Por ejemplo, en las levaduras, el inhibidor α-2 inactiva los genes específicos del tipo a de apareamiento uniéndose como un dímero al activador GRM y a secuencias de ADN que bordean el sitio de unión de GRM.

Inhibidores de la transcripción eucariotas

Ciertos procesos bioquímicos, como el desarrollo embrionario y la regulación del crecimiento celular, dependen de la represión de genes específicos.

Education

Educación

JoVE Core

Molecular Biology

Biología Molecular

Unit 1

Unidad 1

Gene Expression

Expresión génica

KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

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 transcription regulators, activators, co-activators, and co-repressors.

These repression domains are often grouped by their amino acids, such as alanine-rich, glutamine-rich, and proline-rich domains. They can also be described as acidic or basic, and as hydrophilic or hydrophobic. Different repressor domains can often be swapped onto the same DNA-binding domain.

Eukaryotic transcription inhibitors act through three main mechanisms: inhibiting DNA binding, blocking activation, and gene silencing. Inhibiting DNA binding stops an activator from attaching to a promoter or enhancer, or it prevents the transcription initiation complex from binding the transcription start site or the TATA box. This can happen when the inhibitor binds the regulatory site or start site, or when its inhibitory domain interacts with activators, co-activators, or other transcription machinery proteins.

One example is NF-E in humans. It binds the CCAAT box of the fetal gamma-globin gene and blocks the activator CP1 from binding. Blocking activation works differently. The inhibitor can bind next to a promoter or enhancer, as in c-myc regulation, where myc-PRF binds beside the promoter. It can also bind to an activator already attached to DNA. In yeast, GAL80 binds GAL4 when GAL4 is bound to the promoter.

Gene silencing happens when the inhibitor locks or disrupts the transcription initiation complex. It does this by binding both a protein in the machinery and a DNA site near the transcription start site, which anchors the complex. In yeast, the alpha-2 inhibitor works this way to turn off mating type a-specific genes. It binds as a dimer to the activator GRM and to DNA sequences beside the GRM binding site.

How Eukaryotic Gene Repressors Work

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 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

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 eukaryotic gene repressors control transcription through DNA binding, blocking activation, and gene silencing, with clear examples from humans and yeast.

How Eukaryotic Gene Repressors Work | JoVE K12

molecular biology

JoVE Core Biología Molecular presenta los procesos moleculares de la célula a través de lecciones claras y concisas de animaciones audiovisuales. Además, en los vídeos de científicos en acción, se muestran aplicaciones de estos conceptos mediante experimentos reales en laboratorios especializados.

How Eukaryotic Gene Repressors Work

Description

Transcript

Tags