SDS-PAGE analysis of the proteolytic processing of Cry1Ab protoxin by gut extracts from resistant and susceptible insects. Lanes 1 to 3, 1-h incubation; lanes 4 to 6, 24-h incubation; lanes 1 and 4, gut extract from LAB-UK; lanes 2 and 5, gut extract from Cry1Ab-SEL; lanes 3 and 6, gut extract from Cry1Ac-SEL; lane 7, trypsin-activated Cry1Ac control; lane 8, trypsin-activated mutant Cry1Ac control. The molecular weight marker is included in the gel between lanes 6 and 7.