Practice question

Shine-Dalgarno sequence functions during translation initiation in bacteria to recruit ribosome to internal start sites within polycistronic mRNAs. Purine-rich element base-pairs with anti-Shine-Dalgarno of 16S rRNA, increasing local concentration of 30S subunit near AUG, facilitating rapid formation of 30S pre-initiation complex with fMet-tRNAfMet IF2 GTP. Strength and distance of SD to start codon tunes initiation efficiency, enabling differential expression of genes within operon. Eukaryotes lack SD, relying instead on 5' cap scanning and Kozak consensus sequence for start codon selection.