Meselson和Stahl的实验： DNA (14N)DNA (15N) DNA from cells grown in 14N DNA from cells grown in 15N After one generation in 14N After two generations in 14N 2
2025/5/15 11 Meselson和Stahl的实验：
First Second generation generation (a) Conservative: 一 Three DD replication hypotheses Expected density gradient results: DD L'L DD First Second generation generation (b) Semiconservative 一+ DD ↓↓ Expected density gradient results: ①D DD DL First Second generation generation (c) Random dispersive -川+业一++川+川 Mixed Mixed All mixed ↓ Expected density gradient results: D DD DL 25%D:75%L
2025/5/15 12 Three replication hypotheses
a (b)! Generations (CsCl gradient 0 centrifuge) N15 0.3 DNA 0.7 1.0 N14 ■■■ 1.1 1.5 工 1.9 2.5 3.0 4.1 0 and 1.9 mixed Semi-Conservation 0 and 4.1 Replication mixed LUEUIUI IU M.Meselson and F.W.Stahl,Sciences 44:675,1958.13
2025/5/15 13 (CsCl gradient centrifuge) N15 N14 DNA Semi-Conservation Replication M. Meselson and F. W. Stahl, Sciences 44:675, 1958
()Origin,direction and speed of replication 复制的起点、方向和速度 1.Origin of Replication复制起点： 1)Definition:A DNA site at which DNA replication begins and which is essential for proper replication to occur.指DNA复制起始所必 需的一段特殊的DNA序列。 2)Origin composition of several organisms.几种生物 复制起点的组成： ■oric of E.coli: Three 13-mers repeat 3个同向重复的13bp 两种类型的重复序列 序列 Rich in A-T Four nine-mers repeat 2025/5/15 14 4个反向重复的9bp序列
2025/5/15 14 1. Origin of Replication 复制起点： 1) Definition： oriC of E.coli ： 两种类型的重复序列 Three 13-mers repeat 3个同向重复的13bp 序列 Four nine-mers repeat 4个反向重复的9bp序列 Rich in A-T A DNA site at which DNA replication begins and which is essential for proper replication to occur. 指DNA复制起始所必 需的一段特殊的DNA序列。 2) Origin composition of several organisms. 几种生物 复制起点的组成： （二）Origin, direction and speed of replication 复制的起点、方向和速度
Autonomous replication sequence (ARS)of yeast(酵母的自主性复制序列)： Consensus sequence共有序列 功能域A (A/T)TTTAT(A/G)TTT(A/T) 是ARS的核心，可能是起始蛋白结合位点 Two regions A-T rich region,延伸到核心序列3'端 功能域B 50-100bp处 可能是DNA熔解的区域 2025/5/15 15
2025/5/15 15 Autonomous replication sequence (ARS) of yeast（酵母的自主性复制序列）： Two regions 功能域A Consensus sequence 共有序列 （A/T)TTTAT(A/G)TTT(A/T) 是ARS的核心，可能是起始蛋白结合位点 功能域B A-T rich region，延伸到核心序列3’端 50-100bp处 可能是DNA熔解的区域