Zhang Ruifu, Wang Yanling, Leung Pak Chow, Gu Ji-Dong
Laboratory of Environmental Microbiology and Toxicology, Department of Ecology and Biodiversity, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, PR China.
J Microbiol. 2007 Jun;45(3):193-8.
A marine bacterium was isolated from Mai Po Nature Reserve of Hong Kong and identified as Vibrio cholerae MP-1. It contains a small plasmid designated as pVC of 3.8 kb. Four open reading frames (ORFs) are identified on the plasmid, but none of them shows homology to any known protein. Database search indicated that a 440 bp fragment is 96% identical to a fragment found in a small plasmid of another V. cholerae. Further experiments demonstrated that a 2.3 kb EcoRI fragment containing the complete ORF1, partial ORF4 and their intergenic region could self-replicate. Additional analyses revealed that sequence upstream of ORF1 showed the features characteristic of theta type replicons. Protein encoded by ORF1 has two characteristic motifs existed in most replication initiator proteins (Rep): the leucine zipper (LZ) motif located at the N-terminal region and the alpha helix-turn-alpha helix motif (HTH) located at the C-terminal end. The results suggest that pVC replicates via the theta type mechanism and is likely a novel type of theta replicon.
从香港米埔自然保护区分离出一种海洋细菌，鉴定为霍乱弧菌MP-1。它含有一个名为pVC的3.8 kb小质粒。在该质粒上鉴定出四个开放阅读框（ORF），但它们与任何已知蛋白质均无同源性。数据库搜索表明，一个440 bp的片段与在另一种霍乱弧菌的小质粒中发现的片段有96%的同一性。进一步实验表明，一个包含完整ORF1、部分ORF4及其基因间区域的2.3 kb EcoRI片段能够自我复制。额外分析显示，ORF1上游序列具有θ型复制子的特征。ORF1编码的蛋白质在大多数复制起始蛋白（Rep）中存在两个特征基序：位于N端区域的亮氨酸拉链（LZ）基序和位于C端的α螺旋-转角-α螺旋基序（HTH）。结果表明，pVC通过θ型机制复制，可能是一种新型的θ复制子。
