Figure 3. Selective enrichment of RNase R on ribosomes, translating a nonstop mRNA, is dependent on its C-terminal tail.

[A] Ribosomes were enriched for fractions translating the λ-cI nonstop and stop reporter mRNAs and tested for presence of RNase R using western blot analysis. A C-terminal truncation variant of RNase R (RNase R⁷²³) was also tested in this assay. [B] Quantitation of the fold-increase in levels of RNase R on ribosomes translating nonstop message compared to the control stop message. The level of RNase R is higher on enriched ribosomes that are stalled on the defective nonstop reporter mRNA. RNase R^WT enriches more on stalled ribosomes than the C-terminally truncated RNase R⁷²³. This result illustrates that the ribosome enrichment assay is specific and quantitative.