Shine-Dalgarno sequence and expressing proteins * 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)

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.