FIGURE 2.

Effect of single amino acid substitutions on the in vivo function of the Pab1 RRM2 domain. (A) A heat map displaying the enrichment scores (log₂ transformed) of single amino acid substitutions in the RRM2 domain. Each column represents an RRM2 sequence position and each row a substitution to a specific amino acid. An asterisk designates the row of nonsense mutations. Color ranges from blue for the most deleterious mutations to red for the most beneficial ones. Substitutions that were not sequenced in the input or selected pools or that were eliminated by subsequent quality filtration steps are shown in gray; wild-type residues are marked with white dots. The secondary structure of the RRM2 domain aligned to the sequence is shown below the heat map as well as the average enrichment score for each position. (B) The average enrichment scores are projected on the crystal structure of the human RRM2 (PDB_ID 1CVJ). RRM1 and the connecting linker are shown in black and the poly(A) RNA in orange.