SF3B1-mutated PMF patients show distinct aberrant 3′ splicing. (A) SF3B1 mutations were present in 9 PMF patients, both JAK2- and CALR-positive patients. Other splicing factor mutations (U2AF1, SRSF2, and SF3A1) were mutually exclusive to SF3B1. (B) Gene mutation map of SF3B1. Nonsynonymous mutations in SF3B1 were located in oncogenic hotspot sites (K700E and K666N/R/T), with the exception of R594L. Mutations in SF3B1 were overlaid with mutation data from the COSMIC database²²  (y-axis counts at the bottom). (C) Comparison of the frequencies of novel 3′ss and novel 5′ss. (D) Bar graphs showing the frequency of the log2 distance (in nucleotides) of the aberrant splice site from its canonical site. Zero indicates the start of the exon. (E) Hierarchical clustering of log₂-normalized z-scores for 271 significantly upregulated 3′ss sites, located 10 to 30 bp away from the canonical splice site, in SF3B1+ patients (supplemental Table 14). (F) Mutation-specific splicing patterns were observed for amino acid changes K700 and K666.