Construction of a Vector for the Constitutive Expression of Human Papilloma Virus type 16 Genes in Salmonella Enterica Serovar Typhi Strain Ty21a

Salmonella enterica Serovar Typhi strain Ty21a (S. Typhi Ty21a) is the only licensed liveattenuated oral vaccine against Typhoid fever in humans. It is also an oral delivery vehicle for heterologous antigen administration. This article describes the development of a constitutive expression vector, pSalEx, which is derived from pBR322 based vector, pProEx-HTb, for inducible expression of genes in E. coli. Repressor element, lac I, was removed from pProEx-HTb using PCR and restriction digestion. The pSalEx vector is smaller compared to the parent vector, pProEx-HTb, allowing larger inserts to be cloned and expressed. Expression of the major capsid protein (L1) of HPV16 under P_trc promoter of pSalEx was comparable to the constitutive expression of HPV16L1 from the pFS14nsd under the strong P_tac promoter. We demonstrate that pSalEx may be used for expression of heterologous genes in Ty21a and generally in other strains and species of bacteria belonging to the family Enterobacteriaceae.