Supplementary Figure 5: Domain composition and evolutionary features of Xrn1.

(a) Scheme highlighting the strictly structure-based domain composition of S. cerevisiae Xrn1. Parts missing in the ribosome-bound Xrn1 are indicated as dashed line. (b) Model of ribosome-bound S.c. Xrn1 color coded for domains according to the diagram in (a). (c-d) Overlays of the S.c. Xrn1structure with D. melanogaster Xrn1 (c) and the K. lactis Xrn1 (d). KOW, SH3-like and winged helix domains are not visible in the ribosome-bound Xrn1 structure. The 60S ID interspersing the two conserved regions (CR) is missing in the D. melanogaster structure and is rearranged with respect to the K. lactis structure. (e) Ribosome-bound S.c. Xrn1 colored according to sequence identity 10–100% based on multiple sequence alignment (Supplementary Note 1). The 60S ID is the most evolutionarily variable domain in the structure. (f) Excerpt of the secondary structure diagram of S. cerevisiae 28S rRNA showing expansion segment ES31a (highlighted in blue). Structural model below shows the S.c. ribosome–Xrn1 complex. (g) Secondary structure scheme of the D. melanogaster ES31a (highlighted in blue) and the structure of D. melanogaster ribosome with superimposed S.c. Xrn1. 60S ID domain would clash with long ES31a indicating co-evolution of Xrn1 with its rRNA interaction partner.