5' coding sequence responsible for high level expression of X protein of hepatitis B virus in E. coli

Abstract

Three recombinant vectors were constructed to express the X open reading frame of hepatitis B virus in E. coli. All the expression vectors carried in common the tac promoter, sequence encoding X protein from 10th amino acid residues, and the lacZ sequence fused in frame with X. The variation was located at the 5' coding region of the fusion gene. Upon induction, the X-/9-galactosidase fusion proteins encoded by pTXZ2 plasmid only accumulated substantially inside the cells. Analysis of predicted mRNA secondary structures of the X-lacZ fusion genes in three different plasmids suggest that accesibility to ribosome is important to maximal expression. Furthermore we found that the steady state level of X-lacZ mRNA in each recombinant cells was correlated with the level of the fusion protein expressed. These observations are consistent with a model that appropriate binding of ribosome is important for protecting mRNA from degradation.