S and shifting of the peptide signals by different RNA fragments masses are annotated and highlighted as bold letter. Proposed schematic illustration structures for peptide-RNA cross-links along with and without cross-link product of 152 Da mass are shown on the right side of each corresponding spectrum. Fragmentation of RNA refers as yr1, xr1, wr1 and yr2 by McLuckey et al. (61). E, Mapping of ML