1、Chapter 11Phage strategies11.1 Introduction11.2 Lytic development is divided into two periods11.3 Lytic development is controlled by a cascade11.4 Functional clustering in phages T7 and T411.5 Lambda immediate early and delayed genes are needed for both lysogeny and the lytic cycle11.6 The lytic cyc
2、le depends on antitermination11.7 Lysogeny is maintained by repressor protein11.8 Repressor maintains an autogenous circuit11.9 The repressor and its operators define the immunity region11.10 The DNA-binding form of repressor is a dimer 11.11 Repressor uses a helix-turn-helix motif to bind DNA11.12
3、Repressor dimers bind cooperatively to the operator11.13 Repressor at OR2 interacts with RNA polymerase at PRM11.14 The cII and cIII genes are needed to establish lysogeny11.15 PRE is a poor promoter that requires cII protein11.16 Lysogeny requires several events11.17 The cro repressor is needed for
4、 lytic infection11.18 What determines the balance between lysogenic and the lytic cycle?Episome is a plasmid able to integrate into bacterial DNA. EpistasisImmunity in phages refers to the ability of a prophage to prevent another phage of the same type from infecting a cell. It results from the synt
5、hesis of phage repressor by the prophage genome.Induction refers to the ability of bacteria (or yeast) to synthesize certain enzymes only when their substrates are present; applied to gene expression, refers to switching on transcription as a result of interaction of the inducer with the regulator p
6、rotein.Lysogeny describes the ability of a phage to survive in a bacterium as a stable prophage component of the bacterial genome.Lytic infection of bacteria by a phage ends in destruction of bacteria and release of progeny phage.Plasmid is an autonomous self-replicating extrachromosomal circular DN
7、A.Prophage is a phage genome covalently integrated as a linear part of the bacterial chromosome.11.1 IntroductionFigure 11.1 Lytic development involves the reproduction of phage particles with destruction of the host bacterium, but lysogenic existence allows the phage genome to be carried as part of
8、 the bacterial genetic information. 11.1 IntroductionFigure 11.2 Several types of independent genetic units exist in bacteria. 11.1 IntroductionFigure 11.3 Lytic development takes place by producing phage genomes and protein particles that are assembled into progeny phages. 11.2 Lytic development is
9、 controlled by a cascade Figure 11.4 Phage lytic development proceeds by a regulatory cascade, in which a gene product at each stage is needed for expression of the genes at the next stage. 11.2 Lytic development is controlled by a cascade Figure 9.31 Switches in transcriptional specificity can be c
10、ontrolled at initiation or termination. 11.2 Lytic development is controlled by a cascade Figure 11.5 Phage T7 contains three classes of genes that are expressed sequentially. The genome is 38 kb. 11.3 Functional clustering in phages T7 and T4 Essential genes are indicated by numbers. Nonessential g
11、enes are identified by letters. Only some representative T4 genes are shown on the map. 11.3 Functional clustering in phages T7 and T4 Figure 11.6 The map of T4 is circular. There is extensive clustering of genes coding for components of the phage and processes such as DNA replication, but there is
12、also dispersion of genes coding for a variety of enzymatic and other functions.Figure 11.7 The phage T4 lytic cascade falls into two parts: early and quasi-late functions are concerned with DNA synthesis and gene expression; late functions are concerned with particle assembly. 11.3 Functional cluste
13、ring in phages T7 and T4 Figure 11.24 RNA polymerase binds to PRE only in the presence of CII, which contacts the region around -35. 11.3 Functional clustering in phages T7 and T4 Figure 11.8 The lambda lytic cascade is interlocked with the circuitry for lysogeny.11.4 The lambda lytic cascade relies
14、 on antitermination Figure 11.9 The lambda map shows clustering of related functions. The genome is 48,514 bp. 11.4 The lambda lytic cascade relies on antitermination Figure 11.10 Phage lambda has two early transcription units; in the leftward unit, the upper strand is transcribed toward the left; i
15、n the rightward unit, the lower strand is transcribed toward the right. Promoters are indicated by the shaded red or blue arrowheads. Terminators are indicated by the shaded green boxes. Genes N and cro are the immediate early functions, and are separated from the delayed early genes by the terminat
16、ors. Synthesis of N protein allows RNA polymerase to pass the terminators tL1 to the left and tR1 to the right. 11.4 The lambda lytic cascade relies on antitermination Figure 11.11 Lambda DNA circularizes during infection, so that the late gene cluster is intact in one transcription unit.11.4 The lambda lytic cascade relies on antitermination Immunity in phages refers to the ability of a prophage to prevent another phage of the same type from infecting a cell. It results from the synthesis of ph
