[Characteristics of virus growth factor (VGF) encoded by vaccinia virus Tian Tan strain]

Vaccinia virus growth factor (VGF) is encoded by an early gene located near the border between the terminal inverted repeats and the internal unique region of the viral genome. It has been suggested that secreted VGF may serve to stimulate the metabolism of neighboring uninfected cells, thereby increasing the capacity of these cells to support viral replication. In this study, we cloned and sequenced the VGF gene of vaccinia virus strain Tian Tap. The analytical results indicated that VGF of strain Tian Tan possessed the core sequences of Epidermal growth factor superfamily, and more closely related to that of strain WR than to those of other orthopoxvirus strains. Overall deduced amino acid divergence of 4.3% was observed between Tian Tan and WR VGF protein, while divergences ranged from 10% to 20% compared to other orthopoxviruses strains. Most of the amino acid substitutions were found within signal peptide and transmembrane regions, but were not present in secreted ligand domain. It was striking that the amino acid sequence deduced from the ORF TB22L which located within the right terminal region of genome was identical to VGF protein amino acids 67-140, suggesting that ORF TB22L may be derived from the seconed copy of VGF gene of strain Tian Tan.