Figure 4.

Interactions between mutant npr1 proteins and the bZIP transcription factors. (A) Truncated versions of the NPR1 protein were tested for their interactions with AHBP-1b by measuring the β-galactosidase activity resulting from the interactions in yeast. Three independent colonies were taken for each combination, and four measurements were performed on a culture grown from each colony. The mean ± SD is presented. (B) Yeast two-hybrid assay performed by using npr1–1 and npr1–2 point mutants as bait. Yeast cells carrying mutant npr1 and either AHBP-1b or TGA6 were grown for 2 days at 30°C on galactose medium lacking leucine for detection of the LEU2 reporter expression (Left). The same yeast cells also were grown for 2 days at 30°C in medium containing 5-bromo-4-chloro-3-indolyl β-d-galactoside for detection of the β-galactosidase reporter expression (Right). (C) Immunoblot analysis of the expression of npr1 mutant proteins in yeast. Ten micrograms of total yeast protein was loaded in each lane, and immunoblot analysis was carried out by using the NPR1 antiserum.