Synthetic Biology: Engineering Life to Examine It
2016-06-06T00:00:00Z (GMT) by
Two scientific papers that were published in the journal Nature in the year 2000 marked the beginning of engineering biological circuits in cells. The paper Construction of a genetic toggle switch in Escherichia coli (1) by Timothy Gardner, Charles Cantor, and James Collins created a genetic toggle switch by simultaneously introducing an artificial DNA plasmid into a bacterial cell. This DNA plasmid contained two promoters (DNA sequences that regulate the expression of genes) and two repressors (genes that encode for proteins that suppress the expression of genes), as well as a gene encoding for green fluorescent protein that served as a read-out for the system. The repressors used were sensitive to either selected chemicals or temperature. In one of the experiments, the system was turned ON by adding the chemical IPTG (a modified sugar), and nearly all the cells became green fluorescent within five to six hours. Upon raising the temperature to activate the temperature-sensitive repressor, the cells began losing their green fluorescence within an hour and returned to the OFF state. Many labs had used chemical or temperature switches to turn gene expression on in the past, but this paper was the first to assemble multiple genes together and construct a switch that allowed switching cells back and forth between stable ON and OFF states.