虎纹蛙病毒甲基转移酶基因的克隆和分析

经PCR扩增得到虎纹蛙病毒DNA甲基转移酶完整基因片段，并将其克隆到pUCm-T载体，测序可知该基因读码框大小为642bp，编码一由214个氨基酸组成的，预期分子量为24.8kD的多肽。RTV的MTase基因与蛙病毒属的蛙病毒-3型、叉尾Hui病毒和Regina病毒的一致性为96%～97%，与淋巴囊肿病毒属的比目鱼病毒的一致性为56%，从而进一步证明RTV蛙病毒的分类地位；与其它脊椎动物的虹彩病毒一样，该基因包含原核生物5′甲基转移酶的前四个高度保守区而缺少第五个区域，可能只是构成甲基转移酶的一个亚基，RTV、裂唇鱼病毒和大口黑鲈病毒之间MTase基因的一致性与衣壳蛋白基因的差异较大，说明同一种类的不同基因甚至同一基因的不同区域间演化速率不同，因此在虹彩病毒的演化研究中选择合适的基因或基因区域极为重要。

Molecular cloning and sequence analysis of the Rana tigrina ranavirus(RTV) DNA methyltransferase gene

The complete gene of RTV DNA methyltransferase (MTase) was amplified, cloned and sequenced. The ORF consists of 642 bp which codes for a protein of 214 aa with a predicted molecular mass of 24.8kD. Sequence analysis of MTase gene shows much higher identity to the species of genus Ranavirus(96%-97%) than to lymphocystis disease virus(56%),the type species of the genus Lymphocystivirus,indicating again that RTV was the member of the genus Ranavirus; just as the other vertebrate iridoviruses, the MTase gene of RTV contains the first four highly conserved motifs of cytosine MTases but the fifth motif, reponsible for DNA binding specificity, is missing; Among the virus of RTV, doctorfish iridovirus and largemouth bass ranavirus, the very different identity between MTase and MCP gene suggests that the gene used as target to estimate the evolution of the iridoviruses should be suitable.