Efficient cap-dependent translation of polycistronic prokaryotic mRNAs is restricted to the first gene in the operon.

Certain polycistronic prokaryotic mRNAs, when modified at their 5'-termini with a cap structure, are translated as efficiently as, or more efficiently than eukaryotic mRNAs in a eukaryotic cell-free protein synthesising system. However, in this case efficient cap-dependent translation is apparently restricted to the 5'-proximal coding sequence. Moreover, certain translational regulatory signals potentially used by these prokaryotic mRNAs to regulate their levels of expression seem to be recognised by the eukaryotic translational components. The evolutionary significance and practical implications of these results are discussed.