续1λ噬菌体调控

2. immediate early
λ-DNA在宿主细胞环化后，由于DNA分子上没 有任何调控蛋白存在，因此宿主的RNA聚合酶便 分别结合于PL和PR .
Both the lytic and lysogenic pathways require expression of the immediate early and delayed early genes.
• 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
合酶的基因。
• λDNA两条链都有遗传密码，有各自的转
录单位向右转录的叫R链；向左转录的叫 L链。
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.
When lambda DNA enters a new host cell， the lytic and lysogenic pathways start off the same way.
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。
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）。
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;
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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)
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.
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 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 裂解区. 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、早期右向操纵 子以及晚期右向操纵子。
Bacteriophage lambda genome.png
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。 •
λ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 .