Fig. 2. Pcf11p contains a conserved CTD interaction domain. (A) Schematic representation of the domain organization of Pcf11p. The CTD interaction domain is indicated as CID, the segment of 20 consecutive glutamines as Q₂₀, the Rna14p/Rna15p interaction domain as Rna14p/Rna15p ID, the Clp1p-interaction domain as Clp1p ID, and the two zinc-finger motifs as C₂H₂ and C₂HC, respectively. The numbers correspond to the amino acid sequence of Pcf11p. (B) Schematic representation of Pcf11p mutants used in this study. The numbers and letters indicate the length of the amino acid sequence deleted either at the N- or C-terminus. (C) Sequence of the conserved CID of Pcf11p. The amino acid conservation of the CID of Pcf11p was calculated by sequence alignments of 13 known and putative CTD binding proteins containing the CID (results not shown). Invariant residues are in red boxes (100% conservation), blue boxes indicate conserved and similar amino acids that are present in 70–100% of the aligned sequences and yellow boxes indicate conserved and similar residues common in 30–70% of the aligned sequences. Point mutations in pcf11-9 (A66D) and pcf11-13 (D68A, S69A, I70A) changing the CID sequence are marked by arrows.