Fig. 7. Formation of stable α-amanitin-resistant colonies is inhibited by mutation of the C-terminal motif. 293 cells were transfected with α-amanitin-resistant Rpb1 expression plasmids plus a puromycin resistance plasmid (pBiC-S2N+puro), and duplicate plates were selected in α-amanitin or puromycin. Colonies were stained with crystal violet. Deletion (Rpb1ΔC) or scrambling of the C-terminus (Rpb1ΔC+mut Cter) reduced colony numbers relative to constructs with the wild-type C-terminus (Rpb1WT CTD and Rpb1ΔC+WT Cter). Ratios of α-amanitin-resistant/puromycin-resistant colonies determined in an independent experiment from that shown were WT CTD 0.24, Rpb1ΔC+WT Cter 0.30, Rpb1ΔC 0.0032 and Rpb1ΔC+mut Cter 0.0005.