How can bacteria synthesize human insulin?

[haael]

I have just read that genetically modified e. coli can synthesize human insulin.

But I wonder.

Human (eucaryotic) genes have all kinds of introns, regulators, starting sequences etc. Bacteria don't have all of those. How can a procaryota produce an eucaryotic peptide? Has the insulin gene been "flattened" before inserted into e. coli?

 

[Ygggdrasil]

Yes, you are correct that eukaryotic genes have many features that are incompatible with prokaryotes. In order to express a eukaryotic gene in bacteria, you must take only the coding sequence, removing any introns, and regulatory sequences in the untranslated regions, then insert the coding sequence into a plasmid that contains the appropriate regulatory sequences for bacteria. Because eukaryotes and prokaryotes share the same genetic code, bacteria are able to produce the correct amino acid sequence from a eukaryotic DNA sequence (however, tRNA abundances differ between species, so sometimes it is helpful to optimize the codons in the coding sequence by replacing codons for rare E. coli tRNAs with codons for more common E. coli tRNAs).

Of course, this procedure does not always work. Some human proteins (for example, erythropoietin) require specific posttranslational modifications (like glycosylation) that cannot be performed in bacteria. In these cases, eukaryotic expression systems are required.