The sequence of the head-to-tail junction of the HBoV1 episome suggests that HBoV LEH and REH share similarities both in structure and sequence with that of the BPV LEH and MVC REH, respectively [27, 29] . Based on this information [28] , we designed primers to amplify the HBoV1 termini, which are shown in Table 1 and Figure 1 . The Phusion high fidelity PCR kit (NEB, Ipswich, MA) was used following the manufactures' instructions, to amplify the left-end hairpin (LEH) and the rightend hairpin (REH) of HBoV1. Briefly, the DNA denaturation at 98uC for 30 s was followed by 35 cycles of: denaturing at 98uC for 10 s; annealing at 55uC for 15 s; and extension at 72uC for 30 s. Following the final cycle, extension was continued at 72uC for 10 min. The PCR products were analyzed by electrophoresis in a 2% agarose gel. DNA bands were extracted using the QIAquick gel extraction kit (Qiagen, Valencia, CA), and the extracted DNA was directly sequenced at MCLAB (South San Francisco, CA), using primers complementary to the extended sequences on the forward and reverse amplification primers. PCR-generated DNA was cloned in pGEM-T vector (Promega, Madison, WI), and DNAs isolated from cultures of individual clones were subsequently sequenced.