The Ub and M genes were fused using splicing by overlapping extension PCR (SOE-PCR). The Ub and M genes were amplified from pMD-U and pMD-M with the primer pairs Ub-F and Fusion-M-Ub-R and Fusion-M-Ub-F and M-R, respectively ( Table 1 ). The fusion gene product, referred to as Ub-M, was amplified from the purified PCR products with Ub-F and M-R and inserted into the eukaryocyte expression vector pVAX1, and was named pVAX1-Ub-M. The transferring vector pSC11 (our laboratory collection), which is composed of the early promoter P7.5 and late promoter P11 of vaccinia virus, and the LacZ and Amp genes controlled by the promoter P11 as the reporter genes, was used in this study. To construct the transferring vector pSC11-M, the complete M gene was amplified with the pSC11-M-F and pSC11-M-R primer pair (Table 1 ) and inserted into the pSC11. The primer P7.5-F (Table 1) , derived from promoter P7.5 sequence, was used for directional identification and the positive clones, which were subsequently named pSC11-M.