FIG. 3.

Colony filter-lift assay to identify the specificity of interaction between NifL and NifA. In these experiments, the strains of S. cerevisiae CG1945 carrying different combinations of plasmids were grown on SD plates lacking Trp and Leu and were transferred to a Whatman no. 5 paper filter. Cells were permeabilized by freeze-thaw treatment of the filters (freezing in liquid nitrogen and allowing them to thaw at room temperature). The filters carrying the cells were then placed over filters presoaked with Z-buffer–X-Gal solution according to the protocols of the MATCHMAKER yeast two-hybrid assay. β-Galactosidase activity was detected only when S. cerevisiae CG1945 contained pBG503 (GAL4 BD:NifL) and pBG504 (GAL4 AD:NifA).