HUMAN FOAMY VIRUS BEL1 PROTEIN PRODUCED IN ESCHERICHIA-COLI AND INSECT CELLS IS BIOLOGICALLY FUNCTIONAL

Abstract

The Bell protein of human foamy virus (HFV) is a transcriptional transactivator that activates gene expression directed by the homologous long terminal repeat (LTR) and human immuno-deficiency virus type 1 LTR. Here, we overexpressed and purified the wild type and several transactivation-deficient mutant Bell proteins in Escherichia coli as maltose binding protein fusion proteins, The wild type Bell protein, but not mutant proteins, is shown to function efficiently in transactivating the HFV LTR-linked chloramphenicol acetyltransferase gene by protein uptake experiment. In addition, Bell is expressed as a 36 kDa protein in insect cells by the baculovirus expression system, featuring the same molecular weight as that of HFV-infected cells. The experiment of the cell fusion between baculovirus-infected Sf9 cells and COS-7 cells demonstrates that the Bell protein expressed in insect cells is capable of activating HFV LTR-directed gene expression.