Polyadenylation signal facilitates the expression of foreign gene that is driven by an internal promoter located in the reverse orientation to long terminal repeat of retrovirus.

We examined whether the presence of a polyadenylation [poly(A)] signal in a retrovirus vector could affect the expression level of exogenous gene(s) that was controlled by an internal promoter. Three suicide genes were placed under a promoter of the human midkine gene, whose expression is elevated in lung cancer cells. Orientation of the internal transcriptional unit was designed to be opposite to the viral long terminal repeat. Expression of each suicide gene was greater in ecotropic packaging cells transfected with a retrovirus vector without a poly(A) signal than in those with a poly(A)-containing vector. Sensitivity to ganciclovir, a prodrug that becomes an active drug by herpes simplex virus-thymidine kinase, was significantly improved in retrovirally transduced lung cancer cells compared with wild-type cells. However, the sensitivity was much greater in the cells transduced with poly(A)-containing vector than in those with poly(A)-deleted construct. The presence of a poly(A) signal downstream of exogenous gene(s) therefore favors the expression of foreign gene(s) driven by an internal promoter.