For stop codons to be relevant the first step would have to be to transcribe the synthetic DNA into RNA, which would require the presence of adequate promoter s

For stop codons to be relevant the first step would have to be to transcribe the synthetic DNA into RNA, which would require the presence of adequate promoter sequences. Given their complexity and spacing, this would already be quite unlikely — so most of that DNA would never produce RNA. But actual gene expression isn’t the only side-effect of introducing random sequences (although it would be by far the most severe): The synthetic sequences might also contain spurious regulatory motifs, or destroy the spacing of existing regulatory regions (not to mention that altogether random insertions would potentially destroy existing coding sequences). At any rate, this is all purely academic since it makes very little sense to inject synthetic data DNA in living cells: Living cells have a very xenophobic attitude towards foreign DNA (as they see it as potentially viral) and try to destroy it. Once that’s solved, the synthetic data DNA now sits in a cell. Wet, and full of enzymes. These are actually not very good conditions for DNA molecules to persist. Cells age and die, and fragment their own DNA in the process. Or if they don’t, they copy the DNA and, while doing so, introduce errors. No; DNA as a storage medium for data makes most sense when it is dried up and frozen. Better yet, vitrified (but so far there’s no way of undoing DNA vitrification without damaging it.