Bacteria can't read a eukaryotic promoter
- The idea
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- Why
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The idea
“A gene's own promoter switches it on wherever it goes, so it will work in bacteria too.”
The genetic code is nearly universal, so it's easy to assume a piece of DNA works in any cell. The signals that start transcription are a different story.
The short version
The mistake: A gene's own promoter switches it on wherever it goes, so it will work in bacteria too.
What's actually true: RNA polymerase starts only at promoters it recognizes. Bacterial RNA polymerase reads bacterial promoters, not eukaryotic ones.
- A promoter is the stretch of DNA in front of a gene where RNA polymerase binds to start transcription.
- Bacteria and eukaryotes use different promoter sequences. Eukaryotic promoters also need transcription factors that bacteria don't make.
- So to make a human protein in E. coli, biologists put a bacterial promoter in front of the human coding sequence. Ribosomes then translate the mRNA.
On the exam: A promoter works only if the cell's RNA polymerase recognizes it. Bacteria and eukaryotes read different ones.