Recently, we identified a novel human virus with a circular DNA genome of 3.2 kb, tentatively designated as torque teno midi virus (TTMDV), with a genomic organization resembling those of torque teno virus (TTV) of 3.8-3.9 kb and torque teno mini virus (TTMV) of 2.8-2.9 kb. To investigate the extent of genomic variability of TTMDV genomes, the full-length sequence was determined for 15 TTMDV isolates obtained from viremic individuals in Japan. The 15 TTMDV isolates comprised 3175-3230 bases and shared 67.0-90.3% identities with each other, and were only 68.4-73.0% identical to the 3 reported TTMDV isolates over the entire genome. TTMDV possessed a genomic organization with four open reading frames (ORF1-ORF4) with characteristic sequence motifs and stem and loop structures with high GC content, similar to TTV and TTMV. The total of 18 TTMDV genomes differed by up to 60.7% from each other in the amino acid sequence of ORF1 (658-677 amino acids), but segregated phylogenetically into the same cluster, which was distantly related to the TTVs and TTMVs. These results indicate that TTMDV with a circular DNA genome of 3.2 kb, has an extremely high degree of genomic variability, and is classifiable into a third group in the genus Anellovirus.
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