Directly from the source: endogenous preparations of molecular machines

Purification from a source enriched in large macromolecular machines with basic cellular function is still the method of choice in many cases. Such complexes occur in sufficiently high copy numbers in the cell and can be isolated using classical protein purification protocols. Although advanced DNA recombinant technologies and sophisticated overexpression strategies are available, many complexes like the ribosome, RNA polymerase II and membrane protein complexes involved in photosynthesis or in oxidative phosphorylation can only be purified from a rich source. Here, we review recent accomplishments and limitations in applying this strategy.

► Purification of macromolecular machines from source is a widely used strategy. ► The search for the appropriate organism is key in this approach. ► High cellular copy numbers of the macromolecule are required. ► Such machines often exert basic cellular functions. ► Organisms amenable to genetic manipulation are improving traditional isolation methods.