Figure 4. Quantitative analysis of the interaction between each Phd isoform and bSUG1.

The yeast reporter strain CG-1945 was cotransformed with AD-bSUG1 and the indicated BD-Phd isoform plasmid. Yeast transformants were plated on -Leu-Trp plates and incubated at 30 °C for 4 days. The colonies were then pooled in -Leu-Trp-His medium and sonicated for 10 sec. (A) Graph of data from an experiment in which a pool of colonies was seeded at 1,000 cells/ml into selective media with histidine (-Leu-Trp) or without histidine (-Leu-Trp-His). After incubating liquid cultures at 30 °C for 2 days, growth was measured at OD₆₀₀. Data represent the mean ± SD of triplicate assays of a representative experiment and is presented as a percentage of the OD₆₀₀ of yeast grown in selective medium supplemented with histidine (-Leu-Trp). Yeast cells cotransformed with SUG1 and PhLOP1 grew faster than with SUG1 and Phd or PhLP1 (p<0.05). (B) Graph of data from an experiment in which a pool of colonies was collected and prepared for the liquid b-galactosidase reporter assay. Data represent the mean ± SD of two experiments done in triplicate. The b-galactosidase activity is expressed in standard units multiplied by 1,000. The b-galactosidase standard units = 1000 x OD₄₂₀ / time (min) x OD₆₀₀. Yeast cells cotransformed with SUG1 and PhLOP1 had significantly higher b-galactosidase activity than with SUG1 and Phd or PhLP1 (p<0.05).