I've come across some of the NCBI deposited vertebrate mitochondrial sequences where the starting ATC codon is translated as Methionine (eg ND3 MF582632 ).
Thought Methionine is only encoded by a single ATG codon (or ATA in yeast). Is this a mistake or is there any post-transcriptional/translation mechanisms involved?
Mitochondrial genome is quite special case. I faced the same issue when I annotated mitochondrial fungi genome and in fact, some starting codon beside ATG showed up. For instances in humans, AUA and AUU are not rare and GUG and UUG are frequent in prokaryotes.
However and checking briefly the vertebrate mitochondrial DNA, I found Methionine is encoded mainly by AUA and AUG. Nevertheless, in your place, I would make a deep search in papers looking whether ATC did show up in same rare cases as starting codon.
That's really interesting, thank you Loubna Youssar . Some text books need re-writing!
Particularly for the start codon in some bacterial genes it's not uncommon to see start codons which don't use ATG.
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