Asymmetric RNA missplicing by distinct SF3B1 mutation hotspots. HEK293T cells were transfected with constructs expressing FLAG-SF3B1 variants. Top row is western blotting with anti-SF3B1 antibody, showing FLAG-SF3B1 and endogenous SF3B1 at similar levels. End point PCR used isoform-competitive primers, with arrows for canonical (blue), cryptic (red), and heteroduplex (green) forms. Cryptic vs canonical UQCC1 was quantified as a ratio between 2 separate isoform-specific quantitative PCRs.