ID #1816

How does a ribosome distinguish initiator codon from an internal methionine codon in bacteria? I know it uses the shine dalgarno sequence but how does it actually use that sequence. Is the sequence always the same and is it approx. 10 nts. away from the AUG initiator?

    The Shine-Dalgarno sequence is a conserved region meaning that the 16s rRNA in the 30S subunit, this sets up the ribosome in the right place to initiate translation. The 16S rRNA is a single-stranded nucleic acid molecule, and a mRNA is a single-stranded nucleic acid molecule. There is a part of that 16S rRNA that is complementary to that SD sequence, and they hybridize. The AUG (initiator codon) is found about 10 bases away and then translation proceeds. The purpose of the Shine-Dalgarno sequence is just to get the ribosomal subunit in the right place for making the proteins you want.

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