Identification of a new human DNA virus (TTV-like mini virus, TLMV) intermediately related to TT virus and chicken anemia virus

TT virus (TTV) is the only known human virus with single-stranded circular DNA, with a possible but yet unclear relationship to chicken anemia virus ( CAV) of the family Circoviridae. Here we report a new human virus resemblin g TTV and CAV, designated TTV-like mini virus (TLMV). This nonenveloped vir us was smaller (<30 nm) but had a similar density (1.31-1.34 g/ml in CsCl) to TTV, when a TLMV/TTV-coinfected plasma was analyzed. Full-length sequenc ing revealed that the TLMV genome was a circular DNA comprising 2860 nt (is olate CBD231); significantly Shorter than TTV (TA278, 3852 nt) but longer t han CAV (CAECUX1,2319 nt). A strand-specific hybridization assay using olig onucleotide-coated beads suggested TLMV was negative-stranded, like TTV and CAV. In genomic organization, TLMV was similar to both TTV and CAV. The un translated region of TLMV resembled CAV in that both had direct repeats, wh ereas the sequence homology was more evident between TLMV and TTV. The pred icted ORF1 protein of TLMV was rich in R/W/F residues at its amino terminus ; the richness in W was shared by TTV, F by CAV, and R by both, ORF2 protei ns of the three viruses had a common motif, WX7HX3 CXCX5 H. Thus, TLMV is a n intermediate between the remotely related TTV and CAV. Since CAV differs much from other circoviruses, it may better be classified together with TTV and TLMV under a new family: we would coin the Paracircoviridae.