GENE ACTIVATION BY RECRUITMENT OF THE RNA-POLYMERASE-II HOLOENZYME

The single amino acid ''P'' (potentiator) mutation in the holoenzyme c omponent GAL11 creates an interaction between that protein and the dim erization region of GAL4. That interaction triggers strong gene activa tion when the GAL4 fragment is tethered to DNA. Here we show that, amo ng a series of variants of the GAL4 dimerization region and different GAL11P alleles, the strength of the interaction as quantitated in vitr o correlates with the degree of activation in vivo; swapping the prote in fragments bearing the GAL4 dimerization region and the GAL11P mutat ion such that the latter is tethered to DNA and the former is attached to the holoenzyme does not diminish gene activation; gene activation in this system is squelched by overproduction of either a fragment bea ring the GAL4 dimerization region or a fragment of GAL11 bearing a P m utation; and neither GAL11 nor GAL11P is a target of an acidic activat ing region. These results argue that the GAL4-GAL11P interaction trigg ers gene activation simply by recruiting the holoenzyme to DNA. Consis tent with this view, we also show that fusion of LexA to another holoe nzyme component, SRB2, creates an activator, and that an SRB2 mutant p redicted on genetic grounds to interact especially efficiently with a holoenzyme containing a specific mutant form of polymerase also activa tes more efficiently when tethered to DNA.