Figure 4.

KRASinprimarycolorectaltumors.A, RNA-Seq data collected from tumors showing percent abundance of KRAS4A transcripts out of total KRAS (top). Only the tumor sample 01CO008 displayed a KRAS4A proteoform above the threshold for detection by TDMS. The relative abundance of this proteoform (KRAS4A:G12VC180Palm^Farn/Me) was very low compared with the canonical KRAS4B:G12V^Farn/Me proteoform (bottom). B, abundance of mutant KRAS4B in tumors as determined by either RNA-Seq (46) and TDMS. C, fragment ion maps showing that TDMS can distinguish mutant from WT proteoforms within the same tumor. Site of mutation is depicted by colored circles. TDMS, top–down mass spectrometry.