Post on 14-Nov-2018
TranscriçãoI
Roteirodaaula
ü Transcriçãoemprocariotos
ü Operons
ü Regulação
Alberts,5thed
DiferençasentreDNAeRNA
Lehninger,2nded
EstruturasecundáriadoRNA
Alberts,5thed
Transcrição
Alberts,5thed Lehninger,2nded
Transcrição
Alberts,5thed
Direçãodatranscrição(E.coli)
Alberts,5thed
Transcrição–RNApolimerase
Alberts,5thed
RNApolimerase
Alberts,5thed
RNApolimerase
Alberts,5thed
InteraçõesDNA-proteínas
Alberts,5thed
RNApolimerasedeprocariotos
Lehninger,2nded
RNApolimerasedeprocariotos
holoenzima
Lehninger,2nded
Transcriçãoemprocariotos
Alberts,5thed
Reconhecimentodepromotorespordiferentesfatoressigma(σ)
Alberts,5thed
Transcriçãoemprocariotos
• Fatorσ:reconhecimentodediferentespromotores• Distânciaentreoselementosregulatórios:importante
devidoageometriadaRNApolimerase
Regiãopromotora
Lehninger,2nded
Promotoresembactérias
Lehninger,2nded Alberts,5thed
Promotoresembactérias
AdaptadodeLewin,GenesVI
Bactériasvsvírus
Vírusproduzemfatorσsimilaraodebactérias
Alberts,5thed
Elongação
Lewin,GenesVI
Terminadoresemprocariotos
• Intrínsecos:estruturasecundáriaRNA• DependentesdofatorRho
Terminadoresemprocariotos
• Intrínsecos
Lewin,GenesVI
Terminadoresemprocariotos
• DependentedeRho
Lewin,GenesVI
Operon
• TranscriçãodeumclusterdegenesaparKrdeumpromotorúnico
Alberts,5thed
Operontrp
Alberts,5thed
Operontrp
Alberts,5thed
Controledatranscriçãoemprocariotos:atenuação
(a) Two-component system regulating response to low Gin NtrB NtrC
Sensor domain High [G inl Ff®Dm cC
Regulatory domain c:;
His kinase transmitter domain
DNA-binding domain
Low [Ginl Sensor His kinase DNA-binding domain transmitter domain domain --· $ .._ ..L_ATP •
Gin enhancer
(b) General two-component signaling system Sensor Receiver domain domain
Histidine cC I kinase sensor
Sensor domain
His kinase domain
His kinase domain
1 Stimulus Effector domain
• .:Ibfa-C • L ATP G Effect?r
(a) trp leader RNA Translation start codon
Response
Response Regulator
FIGURE 7-5 Two-component regulatory systems. At low cytoplasmic concentrations of glutamine, glutamine dissociates from NtrB, resulting in a conformational change that activates a protein kinase transmitter domain that transfers an ATP "(·phosphate to a conserved histidine (H) in the transmitter domain. This phosphate is then transferred to an aspartic acid (D) in the regulatory domain of the response regulator NtrC. This converts Ntrc into its activated form, which binds the enhancer sites upstream of the ginA promoter (Figure 7-4). (b) General organization of two-component histidyl-aspartyl phospho-relay regulatory systems in bacteria and plants. [Adapted from A. H. West and A.M. Stock, 2001, Trends Biochem. Sci. 26:369.]
its synthesis or for the translation of the encoded proteins when the concentration of tryptophan is high.
However, when the concentration of tRNArrp is not suffi-cient to support a high rate of protein synthesis, the ribosome stalls at the rwo successive Trp codons in region 1 (Figure 7-6b, right). As a consequence, region 2 base-pairs with region 3 as soon as it emerges from the transcribing RNA polymerase. This prevents region 3 from base-pairing with region 4, so the 3-4 hairpin does not form and does not cause pausing by RNA polymerase or transcription termination. As a result, the pro-teins required for tryptophan synthesis are translated by ribo-somes that initiate translation at the start codons for each of these proteins in the long polycistronic Trp mRNA.
Attenuation of transcription elongation also occurs at some operons and single genes encoding enzymes involved in the biosynthes is of other amino acids and metabolites through the function of riboswitches. Riboswitches form RNA tertiary structures that can bind small molecules when they are present at sufficiently high concentration. In some
1 w 100
s·l.....-..!...------t==r.::=J--c:cr--.J....-cx :r-c=:!:::J uuuuul3·
(b) Translation of trp leader
High tryptophan Ribosome covers region 2
5' transcription
UUUUU 3'
FIGURE 7-6 Transcription control by regulation of RNA polymerase elongation and termination in the E. coli Trp operon. (a) Diagram of the 140-nucleotide trp leader RNA. Colored regions are critical to the control of attenuation. (b) Translation of the trp leader sequence begins from the 5' end soon after it is synthesized, while synthesis of the rest of the polycistronic trp mRNA molecule continues.
Low tryptophan Ribosome is stalled at trp codons in region 1
5'
2-3 stem-loop forms
RNA polymerase continues transcription
At high concentrations of amino-acylated tRNA1'P, formation of the 3-4 stem-loop followed by a series of Us causes termination of transcrip-tion. At low amino-acylated tRNA1 'P, region 3 is sequestered in the 2-3 stem-loop and cannot base-pair with region 4. In the absence of the stem-loop structure required for termination, transcription of the trp operon continues. [See C Yanofsky, 1981, Nature 289:751 .]
7.1 Control of Gene Expression in Bacteria 287
Nãocodificaenzimas– sequêncialídercodificandoparaTrp
Alberts,5thedLodisch,7thed
Controledatranscriçãoemprocariotos:atenuação
(a) Two-component system regulating response to low Gin NtrB NtrC
Sensor domain High [G inl Ff®Dm cC
Regulatory domain c:;
His kinase transmitter domain
DNA-binding domain
Low [Ginl Sensor His kinase DNA-binding domain transmitter domain domain --· $ .._ ..L_ATP •
Gin enhancer
(b) General two-component signaling system Sensor Receiver domain domain
Histidine cC I kinase sensor
Sensor domain
His kinase domain
His kinase domain
1 Stimulus Effector domain
• .:Ibfa-C • L ATP G Effect?r
(a) trp leader RNA Translation start codon
Response
Response Regulator
FIGURE 7-5 Two-component regulatory systems. At low cytoplasmic concentrations of glutamine, glutamine dissociates from NtrB, resulting in a conformational change that activates a protein kinase transmitter domain that transfers an ATP "(·phosphate to a conserved histidine (H) in the transmitter domain. This phosphate is then transferred to an aspartic acid (D) in the regulatory domain of the response regulator NtrC. This converts Ntrc into its activated form, which binds the enhancer sites upstream of the ginA promoter (Figure 7-4). (b) General organization of two-component histidyl-aspartyl phospho-relay regulatory systems in bacteria and plants. [Adapted from A. H. West and A.M. Stock, 2001, Trends Biochem. Sci. 26:369.]
its synthesis or for the translation of the encoded proteins when the concentration of tryptophan is high.
However, when the concentration of tRNArrp is not suffi-cient to support a high rate of protein synthesis, the ribosome stalls at the rwo successive Trp codons in region 1 (Figure 7-6b, right). As a consequence, region 2 base-pairs with region 3 as soon as it emerges from the transcribing RNA polymerase. This prevents region 3 from base-pairing with region 4, so the 3-4 hairpin does not form and does not cause pausing by RNA polymerase or transcription termination. As a result, the pro-teins required for tryptophan synthesis are translated by ribo-somes that initiate translation at the start codons for each of these proteins in the long polycistronic Trp mRNA.
Attenuation of transcription elongation also occurs at some operons and single genes encoding enzymes involved in the biosynthes is of other amino acids and metabolites through the function of riboswitches. Riboswitches form RNA tertiary structures that can bind small molecules when they are present at sufficiently high concentration. In some
1 w 100
s·l.....-..!...------t==r.::=J--c:cr--.J....-cx :r-c=:!:::J uuuuul3·
(b) Translation of trp leader
High tryptophan Ribosome covers region 2
5' transcription
UUUUU 3'
FIGURE 7-6 Transcription control by regulation of RNA polymerase elongation and termination in the E. coli Trp operon. (a) Diagram of the 140-nucleotide trp leader RNA. Colored regions are critical to the control of attenuation. (b) Translation of the trp leader sequence begins from the 5' end soon after it is synthesized, while synthesis of the rest of the polycistronic trp mRNA molecule continues.
Low tryptophan Ribosome is stalled at trp codons in region 1
5'
2-3 stem-loop forms
RNA polymerase continues transcription
At high concentrations of amino-acylated tRNA1'P, formation of the 3-4 stem-loop followed by a series of Us causes termination of transcrip-tion. At low amino-acylated tRNA1 'P, region 3 is sequestered in the 2-3 stem-loop and cannot base-pair with region 4. In the absence of the stem-loop structure required for termination, transcription of the trp operon continues. [See C Yanofsky, 1981, Nature 289:751 .]
7.1 Control of Gene Expression in Bacteria 287
RibossomoparaporquenãoencontratRNATrp!
Lodisch,7thed
Operonlac
GlicosexLactose:bactériausaprimeiroaglicose
Alberts,5thed
Operonlac
Alberts,5thed
Operonlac
Alberts,5thed
Reguladoresdatranscrição
Alberts,5thed
Reguladoresdatranscrição
Alberts,5thed
(a) Two-component system regulating response to low Gin NtrB NtrC
Sensor domain High [G inl Ff®Dm cC
Regulatory domain c:;
His kinase transmitter domain
DNA-binding domain
Low [Ginl Sensor His kinase DNA-binding domain transmitter domain domain --· $ .._ ..L_ATP •
Gin enhancer
(b) General two-component signaling system Sensor Receiver domain domain
Histidine cC I kinase sensor
Sensor domain
His kinase domain
His kinase domain
1 Stimulus Effector domain
• .:Ibfa-C • L ATP G Effect?r
(a) trp leader RNA Translation start codon
Response
Response Regulator
FIGURE 7-5 Two-component regulatory systems. At low cytoplasmic concentrations of glutamine, glutamine dissociates from NtrB, resulting in a conformational change that activates a protein kinase transmitter domain that transfers an ATP "(·phosphate to a conserved histidine (H) in the transmitter domain. This phosphate is then transferred to an aspartic acid (D) in the regulatory domain of the response regulator NtrC. This converts Ntrc into its activated form, which binds the enhancer sites upstream of the ginA promoter (Figure 7-4). (b) General organization of two-component histidyl-aspartyl phospho-relay regulatory systems in bacteria and plants. [Adapted from A. H. West and A.M. Stock, 2001, Trends Biochem. Sci. 26:369.]
its synthesis or for the translation of the encoded proteins when the concentration of tryptophan is high.
However, when the concentration of tRNArrp is not suffi-cient to support a high rate of protein synthesis, the ribosome stalls at the rwo successive Trp codons in region 1 (Figure 7-6b, right). As a consequence, region 2 base-pairs with region 3 as soon as it emerges from the transcribing RNA polymerase. This prevents region 3 from base-pairing with region 4, so the 3-4 hairpin does not form and does not cause pausing by RNA polymerase or transcription termination. As a result, the pro-teins required for tryptophan synthesis are translated by ribo-somes that initiate translation at the start codons for each of these proteins in the long polycistronic Trp mRNA.
Attenuation of transcription elongation also occurs at some operons and single genes encoding enzymes involved in the biosynthes is of other amino acids and metabolites through the function of riboswitches. Riboswitches form RNA tertiary structures that can bind small molecules when they are present at sufficiently high concentration. In some
1 w 100
s·l.....-..!...------t==r.::=J--c:cr--.J....-cx :r-c=:!:::J uuuuul3·
(b) Translation of trp leader
High tryptophan Ribosome covers region 2
5' transcription
UUUUU 3'
FIGURE 7-6 Transcription control by regulation of RNA polymerase elongation and termination in the E. coli Trp operon. (a) Diagram of the 140-nucleotide trp leader RNA. Colored regions are critical to the control of attenuation. (b) Translation of the trp leader sequence begins from the 5' end soon after it is synthesized, while synthesis of the rest of the polycistronic trp mRNA molecule continues.
Low tryptophan Ribosome is stalled at trp codons in region 1
5'
2-3 stem-loop forms
RNA polymerase continues transcription
At high concentrations of amino-acylated tRNA1'P, formation of the 3-4 stem-loop followed by a series of Us causes termination of transcrip-tion. At low amino-acylated tRNA1 'P, region 3 is sequestered in the 2-3 stem-loop and cannot base-pair with region 4. In the absence of the stem-loop structure required for termination, transcription of the trp operon continues. [See C Yanofsky, 1981, Nature 289:751 .]
7.1 Control of Gene Expression in Bacteria 287
Reguladoresdatranscrição
Lodisch,7thed
Reguladoresdatranscrição
NtrCaKvatranscriçãoadistância
Alberts,5thed
Rifampicinabloqueiatranscrição
Desenvolvimentodefármacos– processosprocarióKcoseeucarióKcos
Parasabermais
• MolecularBiologyoftheCell–Albertsetal• GenesVI–Lewin• PrinciplesofBiochemistry– Lehninger• MolecularCellBiology-Lodisch