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According to wikipedia and the original complete sequence of the K-12 genome, there are multiple non-AUG start codons such as GUG and UUG. How is this possible? I'm particularly curious about the mechanism of translation initiation in the absence of the canonical tRNAfMet.

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Actually, the start codon, no matter whether it is AUG or GUG/UGG, always encodes for Met. So the translation is initiated by tRNAfMet (prokaryotic translation). The 30s ribosome subunit binds to the Shine-Dalgarno sequence and then it scans the dowstream mRNA sequence for AUG and the tRNA loaded with Met, which has the CAU anticodon form the most stable interaction. But apparently, only two-bases-interaction between the start codon (GUG, UUG) and the fMet-tRNA anticodon are sufficient for the initiation of translation (1). I will look more into the literature.

1. Initiation of translation in prokaryotes and eukaryotes

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Leave it to Marilyn to clarify what everyone else jumbles. I'm seeing some suggestions that there are novel tRNAs with CAC/CAA anticodons. We'll get to the bottom of this. –  bobthejoe Apr 2 '12 at 18:33

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