中国淋巴囊肿病毒胸苷酸合酶基因结构特点及分析

胸苷酸合酶(Thymidylate synthase，TS)是进行DNA合成所必需的酶类，与细胞分化及肿瘤发生密切相关。淋巴囊肿病毒属于虹彩病毒科成员，是能引起百余种淡、海水鱼感染，并产生肿瘤的病毒病原。在已完成中国淋巴囊肿病毒株(Lymphocystis disease virus-China，LCDV-C)基因组序列测定的基础上，本文对位于LCDV-C基因组开放阅读框ORF011L的TS基因结构、及其推定蛋白结构进行了分析。该基因全长858bp，GC含量为28．2％，编码一个长为286aa、分子量为32．7kD、等电点为7．1的推定蛋白，称之为中国淋巴囊肿病毒胸苷酸合酶(LCDV-CTS)。该酶所具有的叶酸结合区在第44和70位氨基酸之间，dUMP结合区在第163和206位氨基酸之间，24个必需氨基酸具有高度保守性。二级结构预测结果显示LCDV-C TS含8个a螺旋，6个β折叠和23个环，表明其具备酶活性分子所有的柔性和可变性结构特征。这是迄今所知在脊椎动物虹彩病毒中唯一含两个完整结合区的TS。对来自包括LCDV在内二十个物种的TS结构进行同源性分析，显示LCDV-C TS被单独分为一枝。进一步对LCDV-C TS可能的起源途径及与宿主的作用等进行了探讨。

Structure Analysis of Thymidylate Synthase Gene from LCDV-C

Thymidylate Synthase (TS) is an enzyme involved in making one of the major building blocks for DNA deoxythymidylic acid (dTMP), and plays a critical role in cell growth and division and is overexpressed in the majority of cancers. Lymphocystis disease virus (LCDV) belong to iridoviridae, and the causative agent of lymphocystis disease, which has been reported to occur in over 100 different fish species worldwide, and viral infection that causes cells to become megaloblastic, thus forming small tumors (bumps or growths). The complete nucleotide sequence of the LCDV-C genome was recently determined. Among the sequenced vertebrate iridoviruses, lymphocystis disease virus isolated from China (LCDV-C) is of the largest genome. Computer-assisted analysis revealed the potential open reading frames ORF 011L of LCDV-C was TS gene, the first report of complete TS gene from vertebrate iridoviruses. The LCDV-C TS gene consists of 858 bp in length with a base composition of 28.2% G C, and encoded a protein of 286 amino acids with a predicted size of 32.7KD. Comparison of the LCDV-C TS to TS from Chilo iridescent virus(CIV), Ambystoma tigrinum virus (ATV) and tiger frog virus (TFV) three iridoviruses and other sixteen species, showed extensive amino acid similarities of TS between four iridoviruses and other species. The predicted LCDV-C TS amino acid sequences contain the folate-binding site in 44-70 residues and dUMP-binding site in 163-206 residues. The secondary structure of LCDV-C TS was predicted with 8 alpha helixes, 6 beta sheets and 23 loops, showed the structure flexible and torsional rotation. Phylogenetic tree was constructed based on the multiple alignments of TS amino acid sequences from twenty species, and LCDV-C TS is a branch alone.