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

The Bell protein of human foamy virus (HFV) is a transcriptional trans activator that activates gene expression directed by the homologous lo ng terminal repeat (LTR) and human immuno-deficiency virus type 1 LTR. Here, we overexpressed and purified the wild type and several transac tivation-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 t he HFV LTR-linked chloramphenicol acetyltransferase gene by protein up take 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 de monstrates that the Bell protein expressed in insect cells is capable of activating HFV LTR-directed gene expression.