sequence inserted into a bacterium, performs a "roll call" of transcription factors. If the results match pre-programmed parameters, it responds by creating a protein that emits a green light supplying a visible sign of a "positive" diagnosis. In follow-up research, the scientists plan to replace the light-emitting protein with one that will affect the cell's fate, for example, a protein that can cause the cell to commit suicide. In this manner, the device will cause only "positively" diagnosed cells to self-destruct. Following the success of the study in bacterial cells, the researchers are planning to test ways of recruiting such bacteria as an efficient system to be conveniently inserted into the human body for medical purposes (which shouldn't be problematic given our natural microbiome; recent research reveals there are already 10 times more bacterial cells in the human body than human cells, that share our body space in a symbiotic fashion). Yet another research goal is to operate a similar system inside human cells, which are much more complex than bacteria. DNA editing Shapiro designed an effective method of synthesizing error-free DNA molecules from error-prone building blocks. DNA programming is the DNA-counterpart of computer programming. The basic computer programming cycle is to modify an existing program, test the modified program, and iterate until the desired behavior is obtained. Similarly, the DNA programming cycle is to modify a DNA molecule, test its resulting behavior, and iterate until the goal (which is either understanding the behavior or improving it) is achieved. One key difference between the two is that unlike computer programming, our understanding of DNA as programming language is very far from being perfect, and therefore trial and error are the norm rather than the exception in DNA-based research and development. Hence DNA programming is more efficient if multiple variants of a DNA program, also called a DNA library, are created and tested in parallel, rather than creating and testing just one program at a time. The basic DNA programming cycle, when operating in full steam, takes the best DNA programs from the previous cycle, uses them as a basis for creating a new set of DNA programs, tests them, and iterates until the goal is achieved. Furthermore, Polymerase Chain Reaction (PCR) is the DNA-equivalent of Gutenberg's movable type printing, both allowing large-scale replication of a piece of text. De novo DNA synthesis is the DNA-equivalent of mechanical typesetting; both ease