Cells must be able to rapidly respond to changes in their external environment — such as temperature or nutrient availability — to exploit and survive in new conditions.
availability 이용할 수 있는
exploit 이용하다
Even cells in a multicellular organism need to respond to developmental cues such as signalling molecules to determine when to divide, migrate or die.
multicellular 다세포의
developmental 발달상의
cues 단서
determine 결정하다
migrate 이동하다
The production of new proteins in response to external stimuli results largely from rapid activation of gene transcription — this is known as inducible gene expression.
stimuli (stimulus 자극제)의 복수형
transcription 표기
Inducible gene expression has several features that distinguish it from the expression of genes that are constitutively active (for example, housekeeping genes). Inducible genes are highly regulated and must be able to be rapidly and specifically activated in response to stimuli.
distinguish 구별하다
constitutively active 구성적 활성
regulated 규제된
Once the stimulus is removed, an inducible gene must quickly return to its basal, inactive state. Furthermore, multiple genes must often be synchronously activated in response to the same stimulus, such that the proteins required to respond to the stimulus are produced simultaneously at the appropriate relative levels.
multiple genes 다중유전자
synchronously 동시에 일어나게
simultaneously 동시에
appropriate 적절한
Similarly, multiple cells in an organism must respond to developmental cues in a coordinated fashion so that the appropriate morphogenetic process occurs over a broad region of cells. Here, we discuss mechanisms of inducible gene expression used by eukaryotic cells.
Similarly 마찬가지로
coordinate 조직화하다
appropriate 적절한
morphogenetic 형태발생의
Although processes that occur following transcription such as protein translation are also regulated as part of inducible gene expression, we do not discuss them in this Review. We focus on the events that are important for recruitment of the transcription machinery and initiation of RNA polymerase II (Pol II)‑dependent transcription.
transcription 표기
translation 변형
recruitment 모집
initiation 개시
Although a traditional model of activator‑dependent recruitment of Pol II and the general transcription factors (GTFs) holds true for many inducible genes, recent studies suggest that Pol II is already present and poised for transcription at many inducible genes.
traditional 전통적인
activator 활성제
recruitment 모집
holds true 유효하다
poise 균형
General transcription factors (GTFs), also known as basal transcriptional factors, are a class of protein transcription factors that bind to specific sites (promoter) on DNA to activate transcription of genetic information from DNA to messenger RNA
Therefore, it is becoming increasingly apparent that there is an additional level of regulation that occurs during the initial stages of transcription elongation before Pol II is released into a productive transcription cycle.
increasingly 점점 더
apparent 분명한
regulation 규제
transcription 표기
elongation 신장( 길이가 증가되는 과정 및 상태)
In addition, several recent studies suggest that some components of signal transduction cascades that lead to inducible gene expression that were once thought to function exclusively in the cytoplasm such as mitogen‑activated protein kinases (MAPKs) are recruited to chromatin and are integral components of transcription complexes.
signal transduction 신호전달
cascade 폭포처럼 흐르다
exclusively 독점적인
chromatin 염색질
integral 필수적인
transcription complexes 전사복합체
MAPK(미토겐 활성화 단백질 키나아제) 경로는 다양한 외부 자극에 대한 세포 반응을 중재하는 데 중요한 역할을 하는 중추적인 신호 전달 계통입니다. 이 경로는 면역 체계의 주요 신호 분자인 염증성 사이토카인의 조절에 복잡하게 관여합니다.
https://www.assaygenie.kr/MAPK-Signaling-in-Inflammatory-Cytokines-Pathways
We use three well‑characterized examples of inducible gene expression to illustrate some of the key mechanisms involved in transcription activation in response to stimuli: Gal gene induction in response to galactose in Saccharomyces cerevisiae, heat‑shock gene induction in Drosophila melanogaster and osmostress regulation in S. cerevisiae.
Transcription activation is an important checkpoint of regulation of gene expression which occurs in response to different intracellular and extracellular signals.
We first discuss the initial steps of the transcription cycle: activator‑dependent recruitment of the transcriptional machinery and the role of co-activators and nucleosome‑remodelling complexes in facilitating this recruitment. We then examine the events that occur following recruitment of the general transcription machinery, including promoter clearance and release of paused Pol II into productive transcription elongation.
transcription cycle 전사주기
recruitment 모집
transcriptional machinery 전사기구
facilitate 가능하게 하다
clearance 없애기
productive 생산하는
transcription elongation 전사 신장
Finally, we examine the role of signalling kinases that seem to play an integral part in multiple aspects of these initial stages of the transcription cycle. Although the mechanisms involved in the chosen examples may not always be observed in all other cases of inducible gene expression, we hope to provide a broad overview of the principles involved in inducible activation of transcription.
multiple 많은
aspect 측면
inducible gene 유도유전자
activator-dependent recruitment
Gene activation involves a multistep recruitment process that consists of several potential rate‑limiting steps during the initial stages of the transcription cycle (reviewed in REF. 8) (FIG. 1).
activation 활성화
multistep 다단계
recruitment 모집
transcription cycle 전사주기
Figure 1 | Early steps in the transcription cycle.
a | Promoter selection is determined by the interaction of one or more transcriptional activator(s) with specific DNA sequences (recognition sites) near target genes. Activators then recruit components of the transcription machinery to these genes through protein–protein interactions. b | Activation of gene expression is induced by the sequential recruitment of large multi‑subunit protein co‑activator complexes (shown in purple and pink) through binding to activators. Activators also recruit ATP‑dependent nucleosome‑remodelling complexes, which move or displace histones at the promoter, facilitating the rapid recruitment and assembly of co‑activators and the general transcription machinery. c | Together, co‑activators and nucleosome remodellers facilitate the rapid recruitment of RNA polymerase II (Pol II) and the general transcription factors (GTFs) TFIIA, TFIIB, TFIID, TFIIE, TFIIF and TFIIH to form the pre‑initiation complex (PIC) on the core promoter9 . These first three steps (a–c) constitute acti‑ vator‑dependent recruitment. d | After PIC assembly, CDK7 in human TFIIH (Kin28 in yeast) phosphorylates the serine 5 (S5) position of the Pol II carboxy‑terminal domain (CTD). At the same time, another subunit of TFIIH, the DNA helicase XPB (Rad25 in yeast), remodels the PIC, and 11–15 bases of DNA at the transcription start site (TSS) is unwound to introduce a single‑stranded DNA template into the active site of Pol II83. Pol II then dissociates from some of the GTFs and transitions into an early elongation stage of transcription83. This step is often referred to as promoter escape or clearance but is not sufficient for efficient passage of Pol II into the remainder of the gene. e | Following promoter clearance, Pol II transcribes 20 – 40 nucleotides into the gene and halts at the promoter‑proximal pause site. Efficient elongation by Pol II requires a second phosphorylation event at the S2 position of the Pol II CTD by CDK9,a subunit of human P‑TEFb (Ctk1 in yeast)8,104. Phosphorylation of the CTD creates binding sites for proteins that are important for mRNA processing and transcription through chromatin such as the histone H3 lysine 36 (H3K36) methylase SET2 (REF. 104). Nucleosome remodellers also facilitate passage of Pol II during the elongation phase of transcription. The transcription cycle continues with elongation of the transcript by Pol II, followed by termination and re‑initiation of a new round of transcription (not shown).
During the initial steps of gene induction, transcriptional activators bind to specific DNA sequences near target genes and recruit transcriptional co‑activators and components of the transcription machinery to these genes through protein–protein interactions.
recruit 모집하다
These steps result in formation of the pre-initiation complex (PIC) on the promoter. For the purposes of this Review, these first three steps can be regarded as a single rate‑determining process, which we refer to as activator‑dependent recruitment (FIG. 1a–c).
be regarded as ~로 여겨지다
rate‑determining process 속도 결정과정
An additional level of regulation is required for polymerase to proceed to productive transcription elongation (FIG. 1d,e). Although all of the steps in the transcription cycle are subject to regulation, we focus in this Review on those steps that are most important for inducible gene expression: activator‑dependent recruitment resulting in PIC formation; activation of the PIC and transcription initiation; and release of paused polymerase into productive elongation.
regulation 규정
Gal4-mediated Gal gene induction in yeast.
The expression of Gal genes, which encode products that are required for the import and metabolism of galactose, is rapidly induced when galactose is added to the growth medium of S. cerevisiae (reviewed in REF. 12).
metabolism 신진대사
Activation of the Gal genes is regulated primarily through activator‑dependent recruitment. Expression is initiated by the transcriptional activator Gal4, which binds to an upstream activating sequence (uASGAl ) in the promoters of Gal genes (FIG. 2).
initiate 개시되게 하다
In yeast, in the absence of galactose, the acidic activator Gal4 is bound by its repressor Gal80 (a). Addition of galactose to the growth medium causes an inducer protein, Gal3, to bind and sequester Gal80 in the cytoplasm, releasing it from Gal4 (b). Gal4 binds target UASGAL (upstream activating sequence) sites in the promoters of Gal genes such as GAL1 and sequentially recruits co‑activators, such as the acetyltransferase SAGA (c) and Mediator (d). Gal4 also recruits ATP‑dependent nucleosome‑remodelling complexes such as SWI/SNF that remove nucleosomes at the promoter and are stimulated by SAGA‑catalysed histone acetylation.Together, SAGA and Mediator recruit RNA polymerase II and the general transcription factors (GTFs), leading to formation of the pre‑initiation complex (PIC) (e). Nucleosome removal, catalysed by SWI/SNF, aids in the kinetics of Mediator and GTF recruitment, thereby facilitating rapid PIC formation and initiation of transcription at Gal genes. H3Ac, histone H3 acetylation; TBP, TATA‑binding protein; TSS, transcription start site
The affinity of Gal4 binding varies among the Gal genes, thereby leading to differential levels of activation. The initiation of the entire response of the Gal regulon to galactose is dependent on this transcriptional activator, Gal4. How then is Gal4 itself regulated? The regions of Gal4 that contain the DNA‑binding and transcription‑activation activities are separable.
affinity 친밀감
initiation 개시
In the absence of galactose, the acidic activation domain of Gal4 is bound tightly by an inhibitor protein Gal80. This prevents the interaction of this domain with co‑activators, such as TATA‑binding protein (TBP) or the SAGA acetyltransferase complex.
When galactose is added to the growth medium, an inducer protein Gal3 sequesters Gal80, alleviating repression of Gal4 and allowing it to interact with and recruit co‑activators to the Gal genes. The activation function of Gal4 is further regulated by post‑translational mechanisms that include phosphorylation and ubiquitin‑mediated degradation.
alleviation 경감, 완화
degradation 저하
Gal gene induction requires co-activators.
In Gal gene induction and many other examples of inducible gene expression, recruitment of co‑activators and the transcription machinery to promoter regions is the key initial step in activating transcription.
recruitment 모집
transcription machinery 전사 기계장치
Recruitment of co‑activators to Gal genes occurs in a sequential but not necessarily interdependent manner. The first co‑ activator to bind to Gal promoters following a shift to galactose‑containing medium is SAGA, which is directly recruited by Gal4 (REFs 22–24).
A few minutes follow‑ ing this, Mediator is recruited to Gal promoters through direct contact with Gal4 (REFs 23,25–28). Finally, Pol II and components of the general transcription machinery, including TBP, TFIIH, TFIIE and TFIIF, are recruited to Gal promoters23. None of these final components, including Pol II, is recruited in the absence of SAGA, which indicates that Gal4 alone is not sufficient to acti‑ vate transcription23,24. Rather, a combination of SAGA and Mediator activities is required for the recruitment of TBP, Pol II and the remainder of the GTFs23,24,29,30. Although this response to galactose might seem specific to yeast and other closely related fungi, the mechanisms by which Gal4 activates gene expression must be widely conserved because Gal4 can activate uASGAl ‑specific transcription in organisms that range from D. melanogaster to humans31,32. Furthermore, SAGA, Mediator and the GTFs are highly conserved from yeast to humans (Supplementary information S1 (figure and tables)). The presence of cis‑regulatory ele‑ ments that have varying affinities for Gal4 at many dif‑ ferent galactose‑inducible genes provides a mechanism to coordinate both the timing and relative levels of expression of the Gal genes. In higher eukaryotes, genes that are co‑regulated often share common cis‑regulatory elements. These regulatory elements can be bound by individual activators or by combinations of transcrip‑ tional activators that have varying affinities. For exam‑ ple, the Forkhead and Ets transcriptional activators bind together to the same DNA motif that is present upstream of a set of co‑regulated genes to synergistically acti‑ vate the transcription of these genes in the developing vascular endothelium33.
https://www.youtube.com/watch?v=By4_yG9Ejqk&list=PLPA6wROIsQ_UVl2HSniieRUUFq8xCsznV&index=12