噬菌体的遗传分析.pptx

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LifecycleandmutantsofphagesGenetic material in a phage一、烈性噬菌体（一、烈性噬菌体（virulentphage）nPhage T4:Structure and life cycle oneofT-evenphagesintricatestructuregeneticmaterialisDNA,linear,about165kb,encodeformorethan150genesLife cyclenLyticdevelopmentiscontrolledbyacascade(裂解周期中基因产物的多级调节)早期早期：由宿主RNA多聚酶转录噬菌体基因，产物主要为RNA多聚酶，因子或反终止因子中中期期：早期基因产物转录中期基因，产物为因子或反终止因子、复制酶等晚期晚期：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分。二、温和噬菌体（temperatephage)nPhage:Structure and life cycle Thegenomeis48514bplineardouble-strandedDNA,formaringafterthephageinjectedintothehostcellthroughthestickyendsclustersofgeneswithrelatedfunctions nLife cycle:lyticcycle(裂解周期）lysogeniccycle（溶源周期）nKey concepts:lysogeny（溶源性）prophage（原噬菌体）lysogenic bacteria or lysogen （溶源菌）Integration of chromosome initiate the lysogenic cycleLysogenicbacteriumareimmunetofurtherinjectionbythesamephageThe repressor protein is responsible for maintaining lysogenic state and for immunity to superinfection Events that damage DNAmay induce prophages toenter the lytic cyclenZygotic induction(合子诱导)Hfr（）F 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 cannot produce a visible colony by platingTheformationofaplaque(acleararea)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）temperaturesensitivemutations（ts）（温度敏感突变）（温度敏感突变）suppressor-sensitivemutations（sus）（抑制因子敏感突变（抑制因子敏感突变）Suppressor-sensitivemutationsnNonsense mutation（无义突变）（无义突变）:琥珀型（amber）：UAG 赭石型（ocher）：UAA 乳白型（opal）：UGA Nonsense mutation is conditional lethal mutation,because the host has nonsense suppressor nNonsense suppressor The nonsense suppressors encoded by altered tRNA genes can insert a specific amino acid at the position of stop codon.Nonsense mutation and nonsense suppressors a,b,c 第二节噬菌体的重组作图Recombinationmappinginbacteriophages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)h can infect only E.coli B when infect a mixture of E.coli B and B-2,plaque of h is distinct,while plaque of h is fuzzy.nr rapidly lyses cells,producing large plaques r slowly lyses cells,producing small plaqueshr h rnFirstly,E.coliBisinfectedwithbothparentalT2phagesnTheprogenyphageisthenspreadontoabacteriallawncomposedofamixtureofE.coliBandB-2nFourplaquetypesappearhr:distinct,smallhr:fuzzy,largehr:fuzzy,smallhr:distinct,large二、T4突变型的三点测验 Three-point cross of phage T4m r tu 负干扰（负干扰（negativeinterference）nInphagecross,negativeinterferenceoftenoccursnGeneticexchangebetweenphagechromosomeswilloccursbefore,during,andafterreplicationnRecombinationisnotrestrictedtoexchangebetweentwochromosomes-threeormoremaybeinvolvedsimultaneously三、X174的遗传分析GeneticanalysisofphageX1741.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：tsC amA amB amA tsC amB 许可温度下，混合感染许可温度下，混合感染su宿主菌宿主菌 子代噬菌体（子代噬菌体（+和和+tsC）许可温度下，感染许可温度下，感染su宿主宿主 限制温度下，感染限制温度下，感染su宿主宿主 +和和+tsC +比较两种噬菌斑比较两种噬菌斑+和和+tsC的数目多少的数目多少 作业：nP141:3,6,7,8,9