Department of Biological Sciences, University of Maryland Baltimore County, Baltimore, MD 21228.
Proc Natl Acad Sci U S A. 1986 Sep;83(18):6761-5. doi: 10.1073/pnas.83.18.6761.
Chloroplast DNA replication in Chlamydomonas reinhardtii is initiated by the formation of a displacement loop (D-loop) at a specific site. One D-loop site with its flanking sequence was cloned in recombinant plasmids SC3-1 and R-13. The sequence of the chloroplast DNA insert in SC3-1, which includes the 0.42-kilobase (kb) D-loop region, as well as 0.2 kb to the 5' end and 0.43 kb to the 3' end of the D-loop region, was determined. The sequence is A+T-rich and contains four large stem-loop stuctures. An open reading frame potentially coding for a polypeptide of 136 amino acids was detected in the D-loop region. One stem-loop structure and two back-to-back prokaryotic-type promoters were mapped within the open reading frame. The 5.5-kb EcoRI fragment cloned in R-13 contains the 1.05-kb SC3-1 insert and its flanking regions. A yeast autonomously replicating (ARS) sequence and an ARC sequence, which promotes autonomous replication in Chlamydomonas, have been mapped within the flanking regions [Vallet, J.-M. & Rochaix, J.-D. (1985) Curr. Genet. 9, 321-324]. Both R-13 and SC3-1 were active as templates in a crude algal preparation that supports DNA synthesis. In this in vitro system, chloroplast DNA synthesis initiated near the D-loop site.
莱茵衣藻叶绿体 DNA 复制是在特定位点形成置换环（D 环）起始的。一个带有侧翼序列的 D 环位点被克隆到重组质粒 SC3-1 和 R-13 中。SC3-1 中的叶绿体 DNA 插入序列，包括 0.42 千碱基（kb）的 D 环区域，以及 D 环区域的 5'端 0.2 kb 和 3'端 0.43 kb，其序列已被确定。该序列富含 A+T，包含四个大的茎环结构。在 D 环区域检测到一个潜在编码 136 个氨基酸多肽的开放阅读框。一个茎环结构和两个背靠背的原核型启动子被映射到开放阅读框内。克隆在 R-13 中的 5.5kb EcoRI 片段包含 1.05kb 的 SC3-1 插入片段及其侧翼区域。酵母自主复制（ARS）序列和促进衣藻自主复制的 ARC 序列已被映射到侧翼区域内[Vallet, J.-M. 和 Rochaix, J.-D.（1985）Curr. Genet. 9, 321-324]。在支持 DNA 合成的粗藻类制备物中，R-13 和 SC3-1 都可作为模板发挥作用。在这个体外系统中，叶绿体 DNA 合成在 D 环位点附近起始。
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