[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.