Borrowing sub-systems from another orgnanism

Engineering a cell is mostly done at the genetic level because that is where the tools are available. However, it is possible to borrow an entire system from another organism, such that the controls of the system are at the genetic level. 

Consider a system with various proteins, including a few transcription factors. Now, lets take the system as a whole and consider the fact that we can control the concentrations of each of the members of the system, and we can take as "output" the concentrations of all the transcription factors in the system. As long as the entire system does not interact with the host machinery, this can be a generic strategy for borrowing systems, rather than genes, from other organisms.