Figure 1.—

Schematic of the tethering assay. (A) The two-plasmid system for the tethering assay. The LEU2-marked plasmid contains the LexA operator–HIS3 reporter. The URA3-marked plasmid contains either LexA–TBP or LexA alone. (B) The wild-type strain or a strain with a deletion in one nonessential gene is transformed with the HIS3 reporter plasmid and the LexA–TBP or LexA plasmid. LexA–TBP binds to the LexA operator in the HIS3 reporter plasmid and results in TBP tethering. HIS3 gene expression is assayed by monitoring cell growth on media containing a competitive inhibitor of the HIS3 gene product, 3-AT.