Table III. Ess1 mutant strains are hypersensitive to CTD truncation alleles.

	Vector	pRPB1	pWT0	pWT9	pA5(15)
Wild type	+++	+++	+++	+++	+++
H164R	++	++	–	–	–
A144T	++	++	–	–	–
Wild type + pESS1	+++	+++	+++	+++	+++
H164R + pESS1	++	++	++	++	++
A144T + pESS1	++	+	++	++	++

Wild-type or ess1^ts mutants (H164R, A144T) were transformed with equal amounts (∼0.2–0.5 µg) of plasmids encoding wild-type or mutant forms of RNA pol II large subunit and grown for 3 days at 30°C. Strains in the bottom half of the table were co-transformed with pESS1 (CEN, HIS3), which encodes wild-type ESS1. Transformation efficiency is summarized as follows: +++ (>10 000); ++ (1001–10 000); + (100–1000); – (<100). Plasmid pRPB1 expresses wild-type Rpb1. A total of eight different CTD mutant plasmids was tested and the results were identical. Representative data for three mutants are shown. Plasmids pWT0, pWT7, pWT8 and pWT9 express truncated RNA pol II derivatives bearing zero, seven, eight or nine copies of the wild-type heptapeptide repeat (YSPTSPS), respectively. Plasmids pA2(18), pE2(15), pA5(15) and pE5(18) express RNA pol II bearing the indicated number of repeats in which Ser2 or Ser5 of the heptad repeat is mutated to alanine (A) or glutamic acid (E). The RPB1 plasmids have been described (West et al., 1995; Yuryev et al., 1996).