续1 λ噬菌体的调控

The three regulators have opposing functions: The cII-cIII pair of regulators is needed to establish the synthesis of repressor. →lysogen The Q regulator is an antitermination factor that allows host RNA polymerase to transcribe the late genes. →lytic
• λ 的整个生命过程都离不开 寄主的RNA
聚合酶 ， 因为 λ 噬菌体没有编码 RNA 聚 因为λ 噬菌体没有编码RNA RNA聚
合酶的基因。 合酶的基因。 • λDNA两条链都有遗传密码，有各自的转 λDNA两条链都有遗传密码 两条链都有遗传密码， 录单位向右转录的叫R 录单位向右转录的叫R链；向左转录的叫 L链。
λ噬菌体的基因表达调控 噬菌体的基因表达调控
λ噬菌体的调控有多种形式，有正调节、 负调节、自主性的反馈调节、抗终止调节、 反义调节及反向调节等。其机制之精巧，过 程之复杂，形式之多样堪为集原核生物调控 之大成。
一、Lamda phage 简介
• λ噬菌体是一种以大肠杆菌为宿主的温
和型噬菌体，它感染大肠杆菌后，通过 精确的基因表达调控机制选择裂解周期 或溶原周期。 • λ噬菌体长48502nt，共61个基因，其中 32个较为重要 .
2) Cro. Cro has dual functions: By binding to OR ( OR3 ) it prevents synthesis of the repressor CI with PRM ; • By interacting with OL (OLl) and OR (ORl)it turns off expression of the immediate early genes (which are not needed later in the lytic cycle （包括自体调控）Cro 浓度较高时。 •
Lytic: three phases - immediate early, delayed early and late （lysis）. Replication of the lambda genome, production of viral coat proteins, and assembly of progeny phage. Lysogenic: three phases - immediate early, delayed early and late （lysogeny）. Repressor protein cI is produced which binds to the two operator regions, OR and OL. Transcription of all lambda genes except cI is stopped. No progeny produced. Phage genome integrates into host genome and becomes prophage. Not disadvantageous for host.
活化P 活化 aQ ：Transcription from PaQ makes a short 60 nt self-terminating transcript which functions in ANTISENSE control of Q expression.
Please Remember: In order to become established as a lysogen in E. coli, bacteriophage lambda must do two things: •repressor must be synthesized •the phage must become integrated into the host chromosome
Figure 12.12 Phage lambda has two early transcription units; in the "leftward" unit, the "upper" strand is transcribed toward the left; in the "rightward" unit, the "lower" strand is transcribed toward the right. . Genes N and cro are separated from the delayed early genes by the terminators. Synthesis of N protein allows RNA polymerase to pass the terminators tL1 to the left and tR1 to the right. 或许这种抗终 止机制的使用是为了保证细 胞中一开始就累积一定量的 Cro蛋白。
虽然int基因也可以由启动子PL 起始转录，但产生的 int mRNA会被细胞中的核酸酶所降解，并不能产生整合酶。 因为由启动子PL起始转录， RNA聚合酶经过N抗终止蛋白 的修饰可以通过终止子tL2，这样RNA得以延伸，形成了核 酸酶的靶位点sib。它首先被RNase 酸酶的靶位点sib。它首先被RNaseⅢ 剪切，接着核酸外切 酶从3′-5′降解mRNA. sib是int基因下游的负调节位点，降解由下游向上游 方向进行，故称其为反向调节（retroregulation）。 反向调节（ ）
Lambda immediate early and delayed early genes are needed for both lysogeny and the lytic cycle
晚早期基因包括 2个复制基因 （裂解感染所需 ），7 的），7个重组 基因（ 基因（有的和裂 解感染中的重组 有关，其中有2 有关，其中有2 个是λDNA λDNA整合 个是λDNA整合 到细菌染色体中 所必需的） 所必需的）及3 个调节基因 （ cⅡ ， cⅢ ， Q）。启动子PL ）。启动子 和操作子OL部分 重叠。 重叠。
3.
delayed early stage The delayed early genes include
two replication genes (needed for lytic infection), seven recombination genes (some involved in recombination during lytic infection, two necessary to integrate lambda DNA into the bacterial chromosome for lysogeny), and three regulators， cII，cIII， Q(位置较靠后）。
Conclusion: CII is essential for lysogeny. Without it -- or without enough of it -- lysogenic growth is not possible.
2) CIII: a chaperone protein that protects CII from host proteases • CII alone has a half-life of < 1 min. • In the presence of CIII, CII has a half-life of ~ 5 min. 3) Q Antiterminator of tR4, allows transcription from PR2 (also called PR') to proceed through to tR5, thus transcribing all of the late lamba structural genes required for phage assembly. But at this stage Q may not exist because CII(基因位 置在Q基因之前） activates PaQ .维基也解说为 Q. 维基也解说为No 维基也解说为
2.1 Lambda has only two immediate early genes, N and cro. 1) N. N codes for an antitermination factor whose action at the nut sites allows transcription to proceed into the delayed early genes;
Bacteriophage lambda genome.png
图中OR1、 2 、3的顺序反了?
When contemplating I suggest attention be payed to the following concepts:
• 时间,空间,量（浓度）, 或然性 • temporal，spatial，amount (concentration)，random(to a certain extent)
4. late lysogeny
CI操纵子 操纵子
cI基因编码的CI阻遏蛋白， cI基因编码的CI阻遏蛋白，分别作用于早 基因编码的CI阻遏蛋白
期左向操纵子和早期右向操纵子中的操作子OL和OR，阻 止这两个操纵子转录. 止这两个操纵子转录.
CI 阻遏蛋白 CI 阻遏蛋白操纵子 与λ噬菌体溶原状态的 确立与维持密切相关。 cI基因突变的λ噬菌体 在生长着大肠杆菌的固 体培养基上总是形成清 晰的噬菌斑，该基因由 此得名。
2. immediate early
λ-DNA在宿主细胞环化后，由于DNA分子上没 DNA在宿主细胞环化后，由于DNA分子上没 在宿主细胞环化后 DNA 有任何调控蛋白存在，因此宿主的RNA聚合酶便 有任何调控蛋白存在，因此宿主的RNA聚合酶便 RNA 分别结合于PL和PR . Both the lytic and lysogenic pathways require expression of the immediate early and delayed early genes. When lambda DNA enters a new host cell， the lytic and lysogenic pathways start off the same way.
λ噬菌体的基因组结构
λ-DNA的基因顺序组织如图所示，按基 DNA的基因顺序组织如图所示， 的基因顺序组织如图所示 因组功能共分六大区域:头部编码区、 因组功能共分六大区域:头部编码区、尾 部编码区、重组区、控制区、复制区和 部编码区、重组区、控制区、 裂解区. 裂解区. 它们分属四个操纵子结构： 它们分属四个操纵子结构：阻遏蛋白操 纵子、早期左向操纵子、 纵子、早期左向操纵子、早期右向操纵 子以及晚期右向操纵子。 子以及晚期右向操纵子。
1) CII CII is a transcription activator. It activates transcription at three promoters: PRE, PI and PaQ. 活化PRE：产生阻遏蛋白CI。稍后进一步介绍。 PRE：产生阻ቤተ መጻሕፍቲ ባይዱ蛋白CI 稍后进一步介绍。 CI。 活化整合酶启动子PI：由PI起始的mRNA在int基因末 端后面约300nt的终点子处停止转录。由PI 转录的mRNA 较为稳定。