Practice question

Shine-Dalgarno sequence AGGAGG located five to nine nucleotides upstream of start codon in bacterial mRNA base-pairs with anti-Shine-Dalgarno CCUCCU at 3' terminus of 16S rRNA in 30S subunit. This RNA-RNA duplex anchors mRNA on ribosome, aligns AUG in P-site for initiator tRNA binding, facilitating 30S pre-initiation complex formation. Strength of pairing modulates translation initiation efficiency across cistrons in polycistronic mRNAs. Eukaryotes lack Shine-Dalgarno, using 5' cap and Kozak context for scanning-dependent initiation instead of internal base-pairing mechanism. This refined regulation supports accurate ribosomal assembly, quality control and translational fidelity under diverse physiological conditions and growth states.