一株输血传播病毒新变种的克隆和序列分析

目的：从1例不明原因转氨酶升高的病人血清中克隆输血传播病毒（TTV）DNA，并进行序列分析。方法：用巢式PCR扩增TTVDNA长片段，连接至pGEM-T载体上，挑选一个克隆（56－B）进行测序，将56－B与GenBank中五株TTV进行氨基酸和核苷酸序列的同源性分析，并用最大似然法进行分子进化分析。结果：56－B株与TA278等五株TTV序列的核苷酸同源性分别为42．4％，48．2％，47．9％，61．7％，氨基酸序列的同源性更低，但其5'，和3'两端非编码区的序列仍然很保守。结论：56－B株与其他TTV株之间的同源性很低，有很高的基因异质性，是TT的一个新变种，代表TTV的一个新的基因型。

Cloning and sequence analysis of a novel TT virus varian]

OBJECTIVE: To clone the DNA of a TT virus (TTV) variant isolated from a patient with elevated alanine transaminase (ALT) of unknown etiology, and conduct sequence analysis. METHODS: The long fragment of TTV DNA was amplified by nested PCR and then cloned into pGEM-T vector. A clone named 56-B containing 3.2 kb TTV DNA was selected for sequence analysis besides homology analysis with other 5 TTV variants retrieved from GenBank, and phylogenetic analysis was carried out by maximum likelihood method. RESULTS: The nucleotide identities of 56-B with the other 5 TTV strains TA278, JA10, US35, SANBAN and TUS01 were 42.4%, 48.2%, 47.9%, 49.8 % and 61.7 % respectively, and the corresponding amino acid identities were even lower. Phylogenetic analysis showed that 56-B was far from other TTV strains in genetic distance that ranged from 0.344 to 0.458. However, the sequences in the 5'- and 3'-end were still much conservative. CONCLUSION: The isolated 56-B showed high heterogeneity in genetic background and was therefore quite distinct from other TTV strains as a novel TTV variant that represents a new TTV genotype.