Slade M B, Chang A C, Williams K L
School of Biological Sciences, Macquarie University, Sydney, New South Wales, Australia.
Plasmid. 1990 Nov;24(3):195-207. doi: 10.1016/0147-619x(90)90003-u.
The complete nucleotide sequence of the plasmid Ddp2 found in the nucleus of the simple eukaryote Dictyostelium discoideum is reported. This 5852-bp plasmid contains a 2661-bp open reading frame (ORF), named the "Rep gene," and 501-bp imperfect inverted repeats. A 1762-bp section of Ddp2, which includes one of the 501-bp repeat sequences, could be deleted without abolishing extrachromosomal replication. Deletion of the second 501-bp repeat, or interruption of the Rep gene, removed the ability to replicate extrachromosomally. We suggest that Ddp2 encodes a protein, "REP," that positively regulates replication initiation, a regulatory mechanism different from that of the yeast 2 mu plasmid which also possesses inverted repeat sequences. Ddp2 has a structure similar to that of plasmid pDG1, found in an unidentified isolate of Dictyostelium, with a similar sized ORF and inverted repeats. A common evolutionary origin is suggested by considerable sequence homology between the ORFs of pDG1 and Ddp2.
报道了在简单真核生物盘基网柄菌细胞核中发现的质粒Ddp2的完整核苷酸序列。这个5852碱基对的质粒包含一个2661碱基对的开放阅读框（ORF），命名为“Rep基因”，以及501碱基对的不完全反向重复序列。Ddp2的一个1762碱基对的片段，包括其中一个501碱基对的重复序列，可以被删除而不影响染色体外复制。删除第二个501碱基对的重复序列，或中断Rep基因，会消除染色体外复制的能力。我们认为Ddp2编码一种蛋白质“REP”，它正向调节复制起始，这是一种不同于酵母2μm质粒的调节机制，酵母2μm质粒也具有反向重复序列。Ddp2的结构与在盘基网柄菌一个未鉴定分离株中发现的质粒pDG1相似，具有相似大小的ORF和反向重复序列。pDG1和Ddp2的ORF之间相当的序列同源性表明它们有共同的进化起源。
