Fig. 2. Dependence of ABI1 and ATHB6 interaction on the functional catalytic domain of PP2C. (A) Specific protein phosphatase activity of purified ABI1, and both point-mutated forms abi1 (ABI1^Gly180Asp) and non-active ABI1^Asp177Ala (NAP) were measured and expressed as relative activities (n = 3, ± SD). (B) The homeodomain (HD) and leucine zipper (ZIP) regions of the AD fusion for ATHB6 (amino acids 1–311) and mutant versions thereof [Δ1 (amino acids 44–311), Δ2 (amino acids 44–217) and S67A (ATHB6^Ser67Ala)] are presented schematically (left panel). They were analysed for binding to DB fusions of ABI1 (A), abi1 (a) and NAP (N) in the yeast two-hybrid system. The β-galactosidase activities for combination with the empty AD vector were subtracted as background from the values presented.