Distribution and frequency of U2AF1 mutations across gene domains and different hematological malignancies. (A) Three isoforms of U2AF1 are shown with the 2 zinc finger domains (ZNF) and the RNA recognition motif (RRM) highlighted. Almost all identified U2AF1 missense mutations are located in 1 of the 2 ZNF domains. (B) Comparison of the frequency of U2AF1 mutations between different hematological malignancies. MDS/MPN and high-risk MDS (RAEB1/2) showed the most frequent mutations (14% and 13%, respectively), whereas primary AML showed the least (6%). RA, refractory anemia; RCMD, refractory cytopenia with multilineage dysplasia; RCMD-RS, refractory cytopenia with multilineage dysplasia with ring sideroblasts; RCUD, refractory cytopenia with unilineage dysplasia.