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  • Shine-Dalgarno sequence present in the prokaryotic mRNA plays a role in initiation of translation. In eukaryotes a Shine-Dalgarno like sequence is present but does not play an important role in initiation of translation.
  • We often try to express a eukaryotic gene in a prokaryote. For example : expressing insulin gene in E.Coli.

My question : If eukaryotes do not have the shine dalgarno sequence , then how can a eukaryotic protein be expressed in a prokaryote ? (I am especially interested in knowing about this in case of cDNA expression)

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Eukaryotes have an analogous sequence called the Kozak sequence. cDNA is easily expressed in prokaryotes by substitution of the Kozak sequence for the Shine-Dalgarno sequence, using standard molecular biology techniques. A caveat is that not all eukaryotic protein will be properly expressed in bacteria because of they lack the ability to carry out post-translational modifications that would occur in a eukaryotic Golgi apparatus (e.g., glycosylation). Insulin is a special case because it is a small, unmodified peptides.

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What are the "standard molecular biology techniques" that you mention in the answer ? –  biogirl Jan 3 at 6:12
    
In this case a simple PCR with the 5' oligonucleotide altered to change the SD sequence. Alternatively, mutagenesis PCR can be used if starting from a circular plasmid ready for expression. –  leonardo Jan 4 at 13:30
    
Ok. Thank you.. –  biogirl Jan 4 at 15:33

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