MAPPING OF ORF121, A FACTOR THAT ACTIVATES BACULOVIRUS EARLY GENE-EXPRESSION

The protein product of the 39k gene of Autographa californica nuclear polyhedrosis Virus is thought to be important for viral replication be cause of its association with the virogenic stroma and its role in act ivation of late gene expression. Transient expression assays showed th at addition of a DNA fragment encoding a 58-amino-acid polypeptide inc reased expression of a 39k reporter plasmid. This stimulation was depe ndent on cotransfection of a plasmid encoding IE1. Cotransfection of t his gene, orf121, also stimulated ief expression, and the activation o f ie I was even more dramatic in the presence of IE1. These data sugge sted that ORF121 stimulated 39k expression by upregulation of IE1 expr ession. Activation of 39k by ORF121 and the viral transcription factor IE2 was additive, while activation by ORF121 and the apoptotic suppre ssor P35 was synergistic. Cotransfection of p39cat and pIE1 with plasm ids encoding ORF121, IE2, and P35 stimulated 39cat expression more tha n 100-fold compared to cells transfected with only p39cat and pIE1. Th ese data suggest that IE2 and ORF121 work by similar mechanisms and in directly activate p39cat by increasing IE1 expression, while P35 incre ases 39cat expression by a different mechanism. (C) 1998 Academic Pres s.