Author response image 1. Analysis of the U6-interacting region of the PRPF8 linker domain using pHMMPGLS analysis.

(A) Stem plot showing the association of individual conserved positions in the U6 snRNA interacting domain of PRPF8 with the 5’SS+4 A to U ratio phenotype in 239 species retaining a detectable PRPF8 ortholog. (B) Boxplot showing the distribution of 5’SS+4 A to U ratio phenotypes for species retaining a PRPF8 ortholog with a Glycine at pHMM alignment position 58, compared to those with a different or unalignable residue at this position (X58). Six of the eight species without a Glycine at this position are from the clade Dipodascaceae and have PRPF8 orthologs that align poorly to the pHMM, suggesting that this position itself may not be specifically important for the +4 phenotype.