Replication eyes can be uni- or bidirectional UNIDIRECTIONAL REPLICATION oRIGIN Replication fork Replicated DNA Parental DNA BIDIRECTIONAL REPLICATION R G Replication fork Replication fork
2.3.3.2环状DNA双链的复制 环状双链DNA的复制可分为0型滚环型和D-环型几种类型。 (1)θ型大肠杆菌基因组的复制原点位于天冬酰胺合酶和ATP合酶操 纵子之间,全长245bp,称为onC。复制的起始点涉及DNA双链的解旋和松 开,形成两个方向相反的复制叉(图2-19)。前导链DNA开始复制前,复制原 点的核酸序列被转录生成短RNA链,作为起始DNA复制的引物。 (2)滚环型( roling circle)这是单向复制的特殊方式。如ΦX174的双 链环状DNA复制型(RF)就是以这种方式复制的。DNA的合成由对正链原点 的专一性切割开始,所形成的自由5′端被从双链环中置换出来并为单链DNA 结合蛋白所覆盖,使其3-OH端在DNA聚合酶的作用下不断延伸。在这个 过程中,单链尾巴的延伸与双链DNA的绕轴旋转同步(图2-20)
The rolling circle replicates DNA Template is circular duplex DNA After 1 revolution displaced strand reaches unit length Initiation occurs on one strand Continued elongation generates displaced strand of multiple unit 3-H lengths 5-P Nick at origin Elongation of growing strand displaces old strand axtwww.eraito.com Figure 13.16 Growing strand The rolling circle generates a multimeric 5 single-stranded tail Download Displaced strand
Rolling circles show in microscopy The rolling circle is a mode Linear single of replication in which a stranded tail eplication fork proceeds around a circular template Circular double for an indefinite number of stranded template revolutions the dna strand newly synthesized in each evolution displaces the strand synthesized in the www.ergito.ce previous revolution giving a tail containing a linear Figure 13.17 A rolling circle appears as a series of sequences circular molecule with a linear tail complementary to the by electron microscopy. Photograph kindly provided by circular template strand Dayid Dressler Download
◼ The rolling circle is a mode of replication in which a replication fork proceeds around a circular template for an indefinite number of revolutions; the DNA strand newly synthesized in each revolution displaces the strand synthesized in the previous revolution, giving a tail containing a linear series of sequences complementary to the circular template strand
3)D-环型(D-lop)这也是一种单向复制的特殊方式。这种方式首 先在动物线粒体DNA的复制中被发现。双链环在固定点解开进行复制。但 两条链的合成是高度不对称的,一条链上迅速合成出互补链,另一条链则成为 游离的单链环(即D-环)