Practice question

During elongation, ribosome encloses about 28 to 30 nucleotides of mRNA as shown by nuclease protection assays and toeprinting. Coverage includes mRNA entry channel, decoding center, P-site and exit channel through small subunit. This 30 nt footprint reflects physical diameter occupying mRNA and predicts spacing between successive ribosomes in polysome to prevent steric collision, typically about 80 nucleotides apart center to center. Knowledge of footprint size underpins ribosome profiling methods that sequence 30 nt fragments to map translational positions genome-wide at codon resolution.