A Recombinant Truncated Cry1Ca Protein Is Toxic to Lepidopteran Insects and Forms Large Cuboidal Crystals in Insect Cells.

A truncated version of the cry1Ca gene from Bacillus thuringiensis was introduced into the genome of Autographa californica multiple nucleopolyhedrovirus (AcMNPV) under the control of two promoters. A recombinant virus (vSyncry1c) was isolated and used to infect insect cells in culture and insect larvae. Structural and ultrastructural analysis of insects infected with vSyncry1C showed the formation of large cuboidal crystals inside the cytoplasm of insect cells in culture and in insect cadavers late in infection. Infected insect cell extracts were analyzed by SDS-PAGE and Western blot and showed the presence of a 65-kDa polypeptide probably corresponding to the protease processed form of the toxin. Bioassays using purified recombinant toxin crystals showed a CL50 of 19.49 ng/ml for 2nd instar A. gemmatalis larvae and 114.1 ng/ml for S. frugiperda. [ABSTRACT FROM AUTHOR]