Fig. 4

Promoter deletion analysis using a β-galactosidase reporter system. a Schematic figure of the promoter region and β-galactosidase activity in the presence or absence of supersaturated silica. The β-galactosidase activity levels are presented as the mean ± standard deviations of three independent experiments and are shown in Miller units. The white and black bars indicate the activity levels in response to 0 and 10 mM silica, respectively. b Image of an SDS-PAGE analysis of expressed proteins from plasmids containing promoter deletion mutants. Cells were harvested from 24 h cultures and disrupted by sonication, after which the soluble fractions were subjected to 12% SDS-PAGE. The black and white arrowheads indicate the bands corresponding to β-galactosidase and silica-induced protein, respectively