In the prokaryote b. subtilis, the rna polymerase holoenzyme binds to a set of promoters when nutrients are readily available, and to a different set of promoters under conditions of nutrient deprivation. the ability of the holoenzyme to bind different promoters under these conditions involves a switch of one subunit. remembering the functions of the rna pol holoenzyme subunits discussed in class, which subunit is most likely to enable this change in promoter binding?