FIG. 3.

Results of the liquid β-galactosidase assay with ONPG as a substrate to demonstrate protein-protein interaction. Miller units were calculated as 1,000 × [OD₄₂₀ − (1.75 × OD₅₅₀)/(t × V × OD₆₀₀)], where t is the elapsed time (in minutes) of incubation, V is 0.1 ml times the concentration factor, and OD₆₀₀ is the absorbance of 1 ml of culture at 600 nm. Assays were repeated a minimum of four times with various cotransformants, and the β-galactosidase activity units shown are an average of four independent observations. Values are means ± standard errors.