页数：60页文件大小：3.34 MB来源： 分子生物学基因Geneppt课件
本课件为《分子生物学》第9章转录（Transcription），依据 Gene VII 教材编排，沿More subunits、Transcription等小节推进，讲解本章核心概念与分子机制，配逐页图示与文字版。
Chapter 9 Transcription
Figure 9.1 The function of RNA polymerase is to copy one strand of duplex DNA into RNA.
Figure 9.2 A transcription unit is a sequence of DNA transcribed into a single RNA, starting at the promoter and ending at the terminator.
Figure 9.3 Transcription takes place in a bubble, in which RNA is synthesized by base pairing with one strand of DNA in the transiently unwound region. As the bubble progresses, the DNA duplex reforms behind it, displacing the RNA in the form of a single poly nucleotide chain.
Figure 9.4 During transcription, the bubble is maintained within bacterial RNA polymerase, which unwinds and rewinds DNA, maintains the conditions of the partner and template DNA strands, and synthesizes RNA.
Figure 9.5 Yeast RNA polymerase has grooves that could be binding sites for nucleic acids. The pink beads show a possible path for DNA that is ~25 Å wide and 5-10 Å deep. The green beads show a narrower channel.
Figure 9.6 Phosphodiester bond formation involves a hydrophilic attack by the 3’-OH group of the last nucleotide of the chain on the 5’ triphosphate of the incoming nucleotide, with release of pyrophosphate.
Figure 9.6 RNA polymerase moves like an inchworm during elongation, when it compresses from the back end and release from the front end.
Figure 9.6 A stalled RNA polymerase can be released by cleaving the 3′end of the transcript.
Figure 9.7 Transcription has four stages, which involve different types of interaction between RNA polymerase and DNA. The enzyme binds to the promoter and melts DNA, remains stationary during initiation, moves along the template durign elongation, and dissociates at termination.
Figure 9.8 Eubacterial RNA polymerases have four types of subunit; a, b, and bhave rather constant sizes in different bacterial species, but svaries more widely.
Sigma factor is the subunit of bacterial RNA polymerase needed for initiation; is the major influence on selection of binding sites (promoters).
Figure 9.9 RNA polymerase passes through several steps prior to elongation. A closed binary complex is converted to an open form and then into a ternary complex.
Figure 9.10 RNA polymerase initially contacts the region from -55 to +20. When sigma dissociates,the core enzyme contracts to -30; when the enzyme moves a few base pairs, it becomes more compactly organized into the general elongation complex.
Figure 9.11 Core enzyme and holoenzyme are distributed on DNA, and very little RNA polymerase is free.
Figure 9.12 How does RNA polymerase find target promoters so rapidly on DNA?.
Figure 9.13 Sigma factor and core enzyme recycle at different points in transcription.
Figure 9.13 Sigma factor and core enzyme recycle at different points in transcription.
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Figure 9.13 Sigma factor and core enzyme recycle at different points in transcription.
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Consensus sequence is an idealized sequence in which each position represents the base most often found when many actual sequences are comp a red.
Figure 1.33 Control sites in DNA provide binding sites for proteins; coding regions are expressed via the synthesis of RNA.
Figure 1.34 A cis-acting site controls the adjacent DNA but does not influence the other allele.
Figure 9.14 A typical promoter has three components, consisting of consensus sequences at -35 and -10, and the startpoint.
Figure 9.9 RNA polymerase passes through several steps prior to elongation. A closed binary complex is converted to an open form and then into a ternary complex.
Footprinting is a technique for identifying the site on DNA bound by some protein by virtue of the protection of bonds in this region against attack by nucleases.
Figure 9.15 Footprinting identifies DNA-binding sites for proteins by their protection against nicking.
Figure 9.10 RNA polymerase initially contacts the region from -55 to +20. When sigma dissociates,the core enzyme contracts to -30; when the enzyme moves a few base pairs, it becomes more compactly organized into the general elongation complex.
Figure 9.16 One face of the promoter contains the contact points for RNA.
Figure 9.3 Transcription takes place in a bubble, in which RNA is synthesized by base pairing with one strand of DNA in the transiently unwound region. As the bubble progresses, the DNA duplex reforms behind it, displacing the RNA in the form of a single poly nucleotide chain.
Figure 9.17 Transcription may generate more tightly wound (positively supercoiled) DNA ahead of RNA polymerase, while the DNA behind becomes less tightly wound (negatively supercoiled).
Figure 14.15 Separation of the strands of a DNA double helix could be achieved by several means.
Figure 9.18 E. coli sigma factors recognize promoters with different consensus sequences. (Numbers in the name of a factor indicate its mass.).
Figure 9.19 A map of the E. colis70 factor identifies conserved regions. Regions 2.1 and 2.2 contact core polymerase, 2.3 is required for melting, and 2.4 and 4.2 contact the -10 and -35 promoter elements.
Figure 9.20 Amino acids in the 2.4 a-helix of s70 contact specific bases in the nontemplate strand of the -10 promoter sequence.
Sporul at ion is the gener at ion of a spore by a bacterium (by morphological conversion) or by a yeast (as the product of meiosis).
Figure 9.21 Transcription of phage SPO1 genes is controlled by two successive substitutions of the sigma factor that change the initiation specificity.
Figure 9.22 Sporul at ion involves the differenti at ion of a vegetative bacterium into a mother cell that is lysed and a spore that is released.
Figure 9.23 Sporul at ion involves successive changes in the sigma factors that control the initiation specificity of RNA polymerase. The cascades in the forespore (left) and the mother cell (right) are related by signals passed across the septum (indicated by horizontal arrows).
Figure 9.24 s Ftriggers synthesis of the next sigma factor in the forespore (sG) and turns on SpoIIR which causes SpoIIGA to cleave pro-sE.
Figure 9.25 The criss-cross regulation of sporul at ion coordinates timing of events in the mother cell and forespore.
Terminator is a sequence of DNA, represented at the end of the transcript, that causes RNA polymerase to terminate transcription.
Figure 9.26 Intr in sic terminators include palindromic regions that form hairpins varying in length from 7-20 bp. The stem-loop structure includes a G-C-rich region and is followed by a run of U residues.
Polarity refers to the effect of a mutation in one gene in influencing the expression (at transcription or translation) of subsequent genes in the same transcription unit.
Figure 9.27 A rho-dependent terminator has a sequence rich in C and poor in G preceding the actual site(s) of termination.9.10 How does rho factor work?.
Figure 9.28 Rho factor pursues RNA polymerase along the RNA and can cause termination when it catches the enzyme pausing at a rho-dependent terminator.9.10 How does rho factor work?.
Figure 9.29 The action of rho factor may create a link between transcription and translation when a rho-dependent terminator lies soon after a nonsense mutation.9.10 How does rho factor work?.
Antitermination proteins allow RNA polymerase to transcri be through certain terminator sites.
Figure 9.30 Antitermination can be used to control transcription by determining whether RNA polymerase terminates or reads through a particular terminator into the following region.
Figure 9.31 Switches in transcriptional specificity can be controlled at initiation or termination.
Figure 9.22 Sporul at ion involves the differenti at ion of a vegetative bacterium into a mother cell that is lysed and a spore that is released.
Figure 9.32 Host RNA polymerase transcribes lambda genes and terminates at t sites. pN allows it to read through terminators in the L and R1 units; pQ allows it to read through the R′terminator. The sites at which pN acts (nut) and at which pQ acts (qut) are located at different relative positions in the transcription units.
Figure 9.33 Ancillary factors bind to RNA polymerase as it passes certain sites. The nutsite consists of two sequences. NusB-S10 join core enzyme as it passes boxA. Then NusA and pN protein bind as polymerase passes boxB. The presence of pN allows the enzyme to read through the terminator, producing a joint mRNA that contains immediate early sequences joined to delayed early sequences.
Figure 9.34 RNA polymerase may alternate between initiation-competent and termination-competent forms as sigma and Nus factors alternatively replace one another on the core enzyme.
Figure 9.34 RNA polymerase may alternate between initiation-competent and termination-competent forms as sigma and Nus factors alternatively replace one another on the core enzyme.
说明：本页源文与上一页完全相同，疑为课件连续两页沿用同一页内容，已按原文保留。
Figure 9.34 RNA polymerase may alternate between initiation-competent and termination-competent forms as sigma and Nus factors alternatively replace one another on the core enzyme.
说明：本页源文与上一页完全相同，疑为课件连续两页沿用同一页内容，已按原文保留。
1.A transcription unit comprises the DNA between a promoter, where transcription initiates, and a terminator, where it ends. 2.Core enzyme has a general affinity for DNA. 3.Bacterial promoters are identified by two short conserved sequences centered at 35 and 10 relative to the startpoint.4.The binary complex is converted to a ternary complex by the incorp or at ion of ribo nucleotide precursors. 5.The "strength" of a promoter describes the frequency at which RNA polymerase initiates transcription.
Summary
6.The core enzyme can be directed to recognize promoters with different consensus sequences by alternative sigma factors.7.The geometry of RNA polymerase-promoter recognition is similar for holoenzymes containing all sigma factors. 8.Bacterial RNA polymerase terminates transcription at two types of sites. Intr in sic terminators contain a GC-rich hairpin followed by a run of U residues.9.The Nus factors increase the efficiency of rho-dependent termination, and provide the means by which antitermination factors act. 10.Antitermination is used by some phages to regulate progression from one stage of gene expression to the next and (less often) in bacteria.
Summary
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