噬菌体的遗传分析ppt课件

1、第五章第五章噬菌体的遗传分析噬菌体的遗传分析BacteriophageGenetics;第一节第一节噬菌体的繁殖和突变型噬菌体的繁殖和突变型Lifecycleandmutantsofphages;Genetic material in a phage;一、烈性噬菌体（一、烈性噬菌体（virulentphage）nPhage T4: Structure and life cyclen one of T-even phagesn intricate structuren genetic material is DNA, linear, about 165 kb, encode for more t

2、han 150 genesn n ;Life cycle;nLyticdevelopmentiscontrolledbyacascaden(裂解周期中基因产物的多级调裂解周期中基因产物的多级调节节)n早期：由宿主早期：由宿主RNA多聚酶转录噬菌多聚酶转录噬菌体基因，产物主要为体基因，产物主要为RNA多聚酶，多聚酶，因因子或反终止因子子或反终止因子n中期：早期基因产物转录中期基因，中期：早期基因产物转录中期基因，产物为产物为因子或反终止因子、复制酶等因子或反终止因子、复制酶等n晚期：中期基因产物转录晚期基因，晚期：中期基因产物转录晚期基因，产物为新的噬菌体组装所需的各个组产物为新的噬菌体组装所需

3、的各个组分。分。;二、温和噬菌体temperate phage)nPhage : Structure and life cyclen n The genome is 48514 bpn linear double-stranded DNA, form a ring after the phage injected into the host cell through the sticky endsn clusters of genes with related functions n ;nLife cycle: n n lytic cycle (裂解周期）n n lysogenic cycle

4、溶源周期）;nKey concepts:n lysogeny溶源性）n prophage原噬菌体）n lysogenic bacteria or lysogenn （溶源菌）;Integration of chromosome initiate the lysogenic cycle;Lysogenic bacterium are immune to further injection by the same phage;The repressor protein is responsible for maintaining lysogenic state and for immunity t

5、o superinfection ;Events that damage DNAmay induce prophages toenter the lytic cycle;nZygotic induction (合子诱导)n n Hfr）Fn Hfr）F（） ;nThe lytic cycle is interlocked with the lysogenic cycle ;三、噬菌体突变型三、噬菌体突变型phagemutants）nPhages are so small that they are visible only under the electron microscopenWe ca

6、nnot produce a visible colony by plating;The formation of a plaque ( a clear area); phage phenotype nPlaque morphology噬菌斑形态突变型 ）nAltered host range宿主范围突变型 ）nConditional lethal （条件致死突变型 ）n temperature sensitive mutations （ts）n （温度敏感突变）n suppressor-sensitive mutationssus）n （抑制因子敏感突变 ） ;Suppressor-sens

7、itivemutationsnNonsense mutation无义突变）:n n 琥珀型amber）：UAGn 赭石型ocher）：UAAn 乳白型opal）：UGA n Nonsense mutation is conditional lethal mutation, because the host has nonsense suppressor ;nNonsense suppressorn The nonsense suppressors encoded by alteredn tRNA genes can insert a specific amino acid n at the p

8、osition of stop codon.n Nonsense mutation and nonsense suppressorsn a, b, c; ;第二节 噬菌体的重组作图Recombination mapping in bacteriophages;一、T2突变型的两点测验 Two-point cross of phage T2 nh can infect two E. coli strains (B and B-2)n h can infect only E. coli B n when infect a mixture of E. coli B and B-2, plaque o

9、f h is distinct, while plaque of h is fuzzy. nr rapidly lyses cells, producing large plaquesn r slowly lyses cells, producing small plaques;hr h rnFirstly, E. coli B is infected with both parental T2 phagesnThe progeny phage is then spread onto a bacterial lawn composed of a mixture of E. coli B and

10、 B-2nFour plaque types appearn ;hr:distinct,smallhr:fuzzy,largehr:fuzzy,smallhr:distinct,largeRF=(h r )(h r ) +total plaques;二、T4突变型的三点测验 Three-point cross of phage T4;m r tu ;负干扰负干扰negativeinterference）nIn phage cross, negative interference often occursnGenetic exchange between phage chromosomes wi

11、ll occurs before, during, and after replicationnRecombination is not restricted to exchange between two chromosomes-three or more may be involved simultaneously ;三、X174的遗传分析Genetic analysis of phage X1741. Two-point cross 突变噬菌体 sus amber1 和 sus amber2 混合感染 su+ amber 宿主菌 子代噬菌体 感染su+宿主菌统计子代噬菌体总数 感染su宿主统计野生型子代的数目 ;2. Three-point cross 通过两点测交已经知道amA与amB之间距离近，而与tsC热敏感突变型距离远，则三者可能的排列顺序为 I： amA amB tsC II：