Figure 1.

Gain-of-function experiments. Various SBG derivatives were analyzed in a plasmid shuffle system. Serially (10-fold) diluted yeast cultures were spotted on plates containing 5-FOA. The extent of cell growth on 5-FOA plates indicates the ability of the yTFIIB derivative to support cell growth (see ref. 22 and text for further details). The same serially diluted cultures were also spotted on plates lacking tryptophan and uracil to estimate the total number of cells analyzed. The actual names of the plasmids expressing the derivatives are indicated in the parentheses.