Augmentation of molecular machines with new functionalities

Molecular machines like DNA/RNA polymerases, ribosomes and enzymes are central to the function of every living cell, underpinning critical tasks covering the expression of the genetic code to coordination of metabolism. When engineering biology there is often the need to supplement these core activities with new functionalities - "augmenting" the biology in a desired way. While fusion with a protein able to provide the new function can sometimes achieve this goal, this approach is inflexible and doesn't offer a quick and easy way to switch the desired function. It is also doesn't generally allow for placement of a new functionality within the structure of the molecular machine itself.