The ribosome distinguishes the initiator AUG codon from other AUG codons that specify methionine residues internally in a protein because there are Shine-Dalgarno sequences just upstream from initiator codons and not upstream of internal methionine codons.

Question

Quizplus · Accepted Answer

The Shine-Dalgarno sequence is a nucleotide sequence in bacterial and archaeal messenger RNA (mRNA) that plays a role in the initiation of protein synthesis by ribosomes. It is located just upstream of the initiator codon AUG, and helps the ribosome recognize and bind to the correct start site. Internal methionine codons lack this Shine-Dalgarno sequence, and are therefore not recognized as initiator codons.

The Ribosome Distinguishes the Initiator AUG Codon from Other AUG