FIG. 4.

Yeast one-hybrid analysis of E1 DNA binding in vivo. Six GAL4AD vectors expressing the AD alone or as a fusion with E1 [AD-E1(F), forward clone; AD-E1(R), reverse clone], E1DBD [AD-E1DBD, forward clone; AD-E1DBD(R), reverse clone], or p53 (AD-p53) were transfected into both the E1BST-LACZ and p53BS-LACZ reporter strains. Individual transformants were regrown on selective medium for 48 h and photographed with an IS1000 digital imaging system (Colonies). The colonies themselves are actually white but appear darkish in the photograph. The colonies were replica transferred to filter paper and tested for β-galactosidase activity with the colony lift filter assay as described in Materials and Methods. The results of the β-galactosidase (β-gal) assay are shown in the right two columns. Three colonies turned blue; these three β-galactosidase-positive clones appear dark in the photo, while the white colonies are not visible.