Regulation of expression of a baculovirus ecdysteroid UDPglucosyltransferase gene.

The Autographa californica nuclear polyhedrosis virus egt gene encodes an ecdysteroid UDPglucosyltransferase which catalyzes the transfer of glucose from UDPglucose to ecdysteroid insect molting hormones. Expression of this gene allows the virus to block molting and pupation of infected insect larvae. In this study, we present the nucleotide sequence of the A. californica nuclear polyhedrosis virus egt gene and characterize egt gene expression at the transcriptional and translational levels. egt was transcribed as two 5'-coterminal mRNAs early in infection. Transferase activity was detected in infected cells and in the extracellular fluid by 3 h after infection. The majority of the activity accumulated in the extracellular fluid. We show that the egt gene product is a 60-kilodalton protein which is secreted from the infected cell. The egt gene is located in a region of the A. californica nuclear polyhedrosis virus genome which exhibited hypervariability in serially passaged virus stocks. Nucleotide sequence analysis revealed that the most common deletion occurring in these serially passaged virus isolates is located in the egt gene.