On March 28, 2013, a team of bioengineers from Stanford University led by Drew Endy announced that they had created the biological equivalent of a transistor, which they named a "transcriptor".  That is, they created a three-terminal device with a logic system that can control other components.  The transcriptor regulates the flow of RNA polymerase across a strand of DNA using special combinations of enzymes to control movement. According to project member Jerome Bonnet, "The choice of enzymes is important. We have been careful to select enzymes that function in bacteria, fungi, plants and animals, so that bio-computers can be engineered within a variety of organisms." 
Transcriptors can replicate traditional AND, OR, NOR, NAND, XOR, and XNOR gates with equivalents, which Endy dubbed "Boolean Integrase Logic (BIL) gates", in a single-layer process (i.e., without requiring multiple instances of the simpler gates to build up more complex ones). Like a traditional transistor, a transcriptor can amplify an input signal.  A group of transcriptors can do almost any type of computing, including counting and comparison.