TRANSACTIVATION OF A CELL HOUSEKEEPING GENE PROMOTER BY THE IE1 GENE-PRODUCT OF BACULOVIRUSES

Protein IE1 is the product of a baculovirus gene, ie1, that is activat ed immediately upon entrance of the viral genome into the cell nucleus . This protein was previously shown to be a trans-regulator of viral g enes whose products are required for initiation of the infectious cycl e including viral DNA replication. To test whether the IE1 protein is also capable of trans-regulating nuclear genes of the host in vitro an d in vivo, we transfected the ie1 gene of Bombyx mori nuclear polyhedr osis virus (BmNPV) into silkworm Bm5 tissue culture cells together wit h expression cassettes directing expression of chloramphenicol acetyl transferase or juvenile hormone esterase under the control of the cyto plasmic actin A3 gene promoter of B. mori. Cotransfection with the ie1 gene resulted in a dramatic increase in the amount of the two enzymes expressed in the transfected cells. The increased enzyme activities c orrelate with an increased accumulation of the corresponding mRNAs, an d the latter is caused by an increase in the rate of transcription dir ected by the cytoplasmic actin gene promoter. The chromosomal cytoplas mic actin gene of Bm5 cells is also upregulated upon transfection of t he cells with the ie1 gene. However, infection of cells with BmNPV doe s not cause an increase in the level of expression of the endogenous c ytoplasmic actin gene. Thus, the effect of IE1 on the transcriptional properties of the cytoplasmic actin gene vary depending on whether IE1 is expressed in isolation or in the context of a viral infection. The trans-activating effects of BmNPV ie1 gene expression on the silkmoth actin promoter are also evident in Spodoptera frugiperda Sf21 and Cho ristoneura fumiferana Cf1 tissue culture cells. Finally, the ie1 gene of Autographa californica nuclear polyhedrosis virus can substitute fo r its BmNPV counterpart in all cell lines tested. (C) 1996 Academic Pr ess, Inc.