Fan W H, Woelfle M A, Mosig G
Department of Molecular Biology, Vanderbilt University, Nashville, TN 37235, USA.
Plant Mol Biol. 1995 Oct;29(1):63-80. doi: 10.1007/BF00019119.
We have characterized two copies of a 2.4 kb DNA element that we call 'Wendy', in the chloroplast chromosome of Chlamydomonas reinhardtii. The two copies of Wendy reside in different single-copy regions at opposite positions in the chloroplast genome. Like many mobile DNA elements, both copies of Wendy are bordered by inverted repeats and contain several additional degenerate copies of these repeat sequences in direct or inverted orientation. In addition, four basepairs are repeated in direct orientation. Two major open reading frames (ORFs) are predicted from the DNA sequence of Wendy I. These ORFs are co-transcribed from a promoter inside the element. The deduced amino acid sequence of the larger of these ORFs shares some weak similarities with sequence motifs of transposases and integrases of other mobile elements. Wendy II appears to be altered relative to Wendy I by point mutations and small deletions and insertions which destroy the ORFs. The leader sequence of the Wendy transcript is nearly identical with the leader sequence of the rbcL transcript of C. reinhardtii, but not of C. moewusii (where the complete Wendy was also undetectable). Furthermore, both copies of Wendy are bracketed by gene clusters that are separated in C. reinhardtii but are contiguous in C. moewusii where they exist in an inverted orientation compared with C. reinhardtii. Wendy was not found in any of the completely sequenced chloroplast genomes of rice, tobacco, pine, Euglena or Marchantia, nor in any other GenBank entry. Our results suggest that Wendy has invaded C. reinhardtii after divergence from other species. Subsequent Wendy-dependent illegitimate homologous or site-specific recombination events or both may have contributed to scrambling of the C. reinhardtii chloroplast genome relative to genomes of other species.
我们对莱茵衣藻叶绿体染色体中一个2.4 kb的DNA元件的两个拷贝进行了特征分析，我们将其称为“温迪”。温迪的两个拷贝位于叶绿体基因组相对位置的不同单拷贝区域。与许多可移动DNA元件一样，温迪的两个拷贝都由反向重复序列界定，并包含这些重复序列的几个额外的简并拷贝，其方向为正向或反向。此外，四个碱基对正向重复。从温迪I的DNA序列预测出两个主要的开放阅读框（ORF）。这些ORF从元件内部的启动子共同转录。这些ORF中较大的那个推导的氨基酸序列与其他可移动元件的转座酶和整合酶的序列基序有一些微弱的相似性。温迪II相对于温迪I似乎因点突变、小的缺失和插入而发生了改变，这些改变破坏了ORF。温迪转录本的前导序列与莱茵衣藻rbcL转录本的前导序列几乎相同，但与牟氏衣藻（在牟氏衣藻中也未检测到完整的温迪）不同。此外，温迪的两个拷贝都被基因簇包围，这些基因簇在莱茵衣藻中是分开的，但在牟氏衣藻中是相邻的，并且与莱茵衣藻相比，它们以反向排列存在。在水稻、烟草、松树、眼虫或地钱的任何已完全测序的叶绿体基因组中，以及在任何其他GenBank条目中都未发现温迪。我们的结果表明，温迪在与其他物种分化后侵入了莱茵衣藻。随后依赖温迪的非法同源或位点特异性重组事件或两者都可能导致了莱茵衣藻叶绿体基因组相对于其他物种基因组的重排。
