Figure 12.

High-resolution native mass spectra of free and internal ribosome entry site (IRES) RNA-bound human 40S subunits. (a) Native mass spectrum of the human 40S subunit acquired with an Orbitrap-UHMR mass analyzer. The well-resolved charge states of three distinct forms of the ribosomal subunit could be detected. The most abundant fully assembled 1.2 MDa 40S particles are labeled in blue, while lower-abundance particles lacking either the S25 or S10 protein are labeled in magenta and red, respectively. (b) Monitoring of the formation of a complex containing human 40S ribosomes and IRES RNA fragments of cricket paralysis virus (CrPV) and hepatits C virus (HCV). The mass spectra of the RNA fragments alone (insets) provide the accurate masses of the IRES elements. Structures of the free 40S ribosomes (PDB entry 5A2Q) and particles bound by CrPV (PDB entry 4V91) and HCV IRES (PDB entry 5A2Q) are shown, with the ribosomal proteins in blue, the rRNA in gray, and the IRES elements in yellow and green, respectively. From ref (53). CC BY 4.0.