噬菌體的遺傳分析ppt課件

1、第五章第五章噬菌體的遺傳分析噬菌體的遺傳分析BacteriophageGenetics;第一節(jié)第一節(jié)噬菌體的繁殖和突變型噬菌體的繁殖和突變型Lifecycleandmutantsofphages;Genetic material in a phage;一、烈性噬菌體（一、烈性噬菌體（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(裂解周期中基因產(chǎn)物的多級調(diào)裂解周期中基因產(chǎn)物的多級調(diào)節(jié)節(jié))n早期：由宿主早期：由宿主RNA多聚酶轉(zhuǎn)錄噬菌多聚酶轉(zhuǎn)錄噬菌體基因，產(chǎn)物主要為體基因，產(chǎn)物主要為RNA多聚酶，多聚酶，因因子或反終止因子子或反終止因子n中期：早期基因產(chǎn)物轉(zhuǎn)錄中期基因，中期：早期基因產(chǎn)物轉(zhuǎn)錄中期基因，產(chǎn)物為產(chǎn)物為因子或反終止因子、復(fù)制酶等因子或反終止因子、復(fù)制酶等n晚期：中期基因產(chǎn)物轉(zhuǎn)錄晚期基因，晚期：中期基因產(chǎn)物轉(zhuǎn)錄晚期基因，產(chǎn)物為新的噬菌體組裝所需的各個組產(chǎn)物為新的噬菌體組裝所需

3、的各個組分。分。;二、溫和噬菌體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原噬菌體）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 (合子誘導(dǎo))n n Hfr）Fn Hfr）F（） ;nThe lytic cycle is interlocked with the lysogenic cycle ;三、噬菌體突變型三、噬菌體突變型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噬菌斑形態(tài)突變型 ）nAltered host range宿主范圍突變型 ）nConditional lethal （條件致死突變型 ）n temperature sensitive mutations （ts）n （溫度敏感突變）n suppressor-sensitive mutationssus）n （抑制因子敏感突變 ） ;Suppressor-sens

7、itivemutationsnNonsense mutation無義突變）: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; ;第二節(jié) 噬菌體的重組作圖Recombination mapping in bacteriophages;一、T2突變型的兩點測驗 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突變型的三點測驗 Three-point cross of phage T4;m r tu ;負(fù)干擾負(fù)干擾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的遺傳分析Genetic analysis of phage X1741. Two-point cross 突變噬菌體 sus amber1 和 sus amber2 混合感染 su+ amber 宿主菌 子代噬菌體 感染su+宿主菌統(tǒng)計子代噬菌體總數(shù) 感染su宿主統(tǒng)計野生型子代的數(shù)目 ;2. Three-point cross 通過兩點測交已經(jīng)知道amA與amB之間距離近，而與tsC熱敏感突變型距離遠，則三者可能的排列順序為 I： amA amB tsC II：