Stassen A P, Schoenmakers E F, Yu M, Schoenmakers J G, Konings R N
Department of Molecular Biology, University of Nijmegen, The Netherlands.
J Mol Evol. 1992 Feb;34(2):141-52. doi: 10.1007/BF00182391.
The nucleotide sequence of the circular single-stranded genome of the filamentous Escherichia coli phage I2-2 has been determined and compared with those of the filamentous E. coli phages Ff(M13, fl, or fd) and IKe. The I2-2 DNA sequence comprises 6744 nucleotides; 139 nucleotides less than that of the N- and I2-plasmid-specific phage IKe, and 337 (336) nucleotides more than that of the F-plasmid-specific phage Ff. Nucleotide sequence comparisons have indicated that I2-2, IKe, and Ff have a similar genetic organization, and that the genomes of I2-2 and IKe are evolutionarily more closely related than those of I2-2 and Ff. The studies have further demonstrated that the I2-2 genome is a composite replicon, composed of only two-thirds of the ancestral genome of IKe. Only a contiguous I2-2 DNA sequence of 4615 nucleotides encompassing not only the coat protein and phage assembly genes, but also the signal required for efficient phage morphogenesis, was found to be significantly homologous to sequences in the genomes of IKe and Ff. No homology was observed between the consecutive DNA sequence that contains the origins for viral and complementary strand replication and the replication genes. Although other explanations cannot be ruled out, our data strongly suggest that the ancestor filamentous phage genome of phages I2-2 and IKe has exchanged its replication module during evolution with that of another replicon, e.g., a plasmid that also replicates via the so-called rolling circle mechanism.
丝状大肠杆菌噬菌体I2 - 2的环状单链基因组的核苷酸序列已被测定，并与丝状大肠杆菌噬菌体Ff（M13、fl或fd）和IKe的核苷酸序列进行了比较。I2 - 2的DNA序列由6744个核苷酸组成；比N - 和I2 - 质粒特异性噬菌体IKe少139个核苷酸，比F - 质粒特异性噬菌体Ff多337（336）个核苷酸。核苷酸序列比较表明，I2 - 2、IKe和Ff具有相似的遗传组织，并且I2 - 2和IKe的基因组在进化上比I2 - 2和Ff的基因组关系更密切。研究进一步证明，I2 - 2基因组是一个复合复制子，仅由IKe祖先基因组的三分之二组成。仅发现一段4615个核苷酸的连续I2 - 2 DNA序列，它不仅包含外壳蛋白和噬菌体组装基因，还包含有效噬菌体形态发生所需的信号，与IKe和Ff基因组中的序列具有显著同源性。在包含病毒和互补链复制起点以及复制基因的连续DNA序列之间未观察到同源性。尽管不能排除其他解释，但我们的数据强烈表明，噬菌体I2 - 2和IKe的祖先丝状噬菌体基因组在进化过程中与另一个复制子（例如，也通过所谓滚环机制复制的质粒）交换了其复制模块。
