The influence of vipA mutations on VipB synthesis and Hcp synthesis/secretion. Deletion mutant alleles (lanes c-d), wild-type (lane e) or substitution mutant alleles (lanes f-r) of vipA were expressed from the ptac promoter of pMMB66EH in a vipA null mutant background. Hcp protein contained in the pellet fraction or secreted to the culture medium was separated by SDS-PAGE and identified by immunoblot analysis using antiserum specific for Hcp. For detection of intrabacterial VipB and VipA, anti-VipB and anti-His antisera were used respectively. The experiment was repeated at least three times and a representative example is shown.