Recombinant DNA technology in eukaryotes

The techniques for gene manipulation, cloning, and expression were first developed in bacteria but are now applied routinely in a variety of model eukaryotes. The genomes of eukaryotes are larger and more complex than those of bacteria, so modifications of the techniques are needed to handle the larger amounts of DNA and the array of different cells and life cycles of eukaryotes. For instance, some eukaryotic proteins cannot be easily expressed in large amounts in bacteria, and eukaryotic expression systems need to be employed. A widely used vector–expression system for eukaryotic proteins is insect baculovirus, into which genes are inserted and expressed at high rates in cultured insect cells,. Although eukaryotic genes are cloned and sequenced in bacterial hosts, it is often desirable to introduce such genes back into the original eukaryotic host or into another eukaryote — in other words, to make a transgenic eukaryote.