Xu W, McFadden B A
Department of Biochemistry and Biophysics, Washington State University, Pullman 99164-4660, USA.
Plasmid. 1997;37(2):95-104. doi: 10.1006/plas.1997.1281.
The cyanobacterium Synechocystis sp. strain PCC 6803 contains several cryptic plasmids of 2.4, 5.2, and about 50 or 100 kbp. The complete nucleotide sequence of the 5.2-kbp plasmid, pCC5.2, has been analyzed and is reported here. This plasmid contains 5214 bp and 53.1% A+T. Six open reading frames, ORFs A-F (encoding peptides of larger than 90 amino acid residues), were located on both strands of pCC5.2. ORF B codes for a potential replication protein containing 971 amino acids, for which there are three homologous proteins encoded by other cyanobacterial plasmids. ORF C encodes a polypeptide of 93 amino acids which shares homologies with products of two ORFs found in the protein database. Counterparts of the products of ORF A, D, E, and F could not be found in the protein database. Detection of a single-stranded DNA intermediate during replication of pCC5.2 indicates that this plasmid may also replicate by a rolling circle mechanism, as has been reported for pCA2.4 and pCB2.4 from the same strain of Synechocystis (PCC 6803).
聚球藻属（Synechocystis）PCC 6803菌株含有几种隐蔽质粒，大小分别为2.4、5.2以及约50或100千碱基对。本文分析并报道了5.2千碱基对质粒pCC5.2的完整核苷酸序列。该质粒含有5214个碱基对，A+T含量为53.1%。在pCC5.2的两条链上定位了六个开放阅读框，即ORF A - F（编码大于90个氨基酸残基的肽）。ORF B编码一种潜在的复制蛋白，含有971个氨基酸，其他蓝藻质粒编码有三种与之同源的蛋白。ORF C编码一个93个氨基酸的多肽，它与蛋白质数据库中发现的两个ORF的产物具有同源性。在蛋白质数据库中未找到ORF A、D、E和F产物的对应物。在pCC5.2复制过程中检测到单链DNA中间体，这表明该质粒可能也通过滚环机制进行复制，就像来自同一聚球藻菌株（PCC 6803）的pCA2.4和pCB2.4所报道的那样。
