The RNA-interacting 3′HP of motif Ib is required for growth in the cold. (A–D) A mutation of the RF dipeptide (R177A) at the tip of the 3′HP compromises growth at low temperature (A versus B) and synergizes with second site mutations in the dipeptide (F178A; B), in the nearby HB domain (P521A; C), and in the opposing, 5′HP bookend (K398A; D). Serial dilutions of yeast strains expressing Prp43p with the indicated mutations were tested for growth on solid rich medium (YPDA) (A–C) or solid minimal medium containing 5-FOA (D) and incubated at the indicated temperatures for 6 d (A), 1 d (B,C), or 3 d (D) to monitor growth. The domains encompassing the mutations are indicated below and color-coded as in Figure 1.
