Characterization of a baculovirus gene encoding a small conotoxinlike polypeptide.

We identified a gene of Autographa californica nuclear polyhedrosis virus (AcMNPV) that encodes a small cysteine-rich polypeptide which has size and sequence similarity to omega-conotoxins, a class of calcium ion (Ca2+) channel inhibitors, found in the venom of cone snails. Transcriptional analysis indicated that the 159-bp open reading frame, which we named ctl, and a downstream 984-bp open reading frame are transcribed as a single 1.3-kb bicistronic late RNA. The mature ctl gene product was identified as a small secreted protein by high-pressure liquid chromatography fractionation of extracellular fluid. Viruses with a site-specific deletion in ctl appeared normal with regard to the kinetics and virulence of infection, both in vitro and in vivo. Although we studied the behavior of wild-type and mutant virus-infected insects in some detail, a biological role for ctl in AcMNPV infection remains to be established.