A smart gene is an artificially constructed genetic molecule (known as a construct) composed of one or more genes encoding a protein to be expressed and a region (such as a promoter) that will only allow the protein to be expressed under specific conditions (such as the presence of a particular molecule). Therefore a smart gene allows conditional expression of the gene it encodes for based on whether specific conditions inside the cell are met. This property makes such constructs as ideal therapeutic vehicles for gene therapy.
Using combinations of smart gene constructs a DNA computer has been designed that is able to trigger gene expression based on the presence of a particular mRNA molecule. Consequently by employing chains of such constructs more sophisticated decision making systems can be produced.