immediateearly baculovirus genes transactivate the p143 gene promoter of autographa californica nuclear polyhedrosis virus transacting regulatory components of autographa californica nuclear polyhedrosis virus acmnpv were studied in a transient assay system for their ability to activate the p143 gene promoter a region including 502 nt upstream of the aug of the p143 gene was linked to the bacterial chloramphenicol acetyltransferase cat gene the p143 promotercat construct was used to identify acmnpv immediateearly gene products required for expression from the p143 gene early promoter transient expression assays in uninfected spodoptera frugiperda cells indicated that the ie1 gene product was capable of transactivating the p143 gene promoter and this activation was augmented by the ien gene product in addition another immediateearly gene pe38 was shown to mediate transactivation of the p143 gene promoter but not the 39k delayed early gene promoter deletions to 187 bp relative to the p143 rna start site did not significantly affect promoter activity in the combined presence of ie1 and the hindiiif fragment however a deletion to 52 bp decreased promoter activity by 40 in contrast in the presence of ts8 dna at 33 degrees deletions to 52 bp decreased promoter activity by 80 suggesting that additional viral factors were involved in p143 gene promoter regulation