Collins' team designed two separate synthetic gene networks not found naturally in E. coli bacteria. Each uses a different method to make the bacteria count.
The first, the Riboregulated Transcriptional Cascade (RTC) synthetic gene network, counts by starting and stopping transcription and translation the process by which a gene's instructions are executed of a series of genes every time an event occurs. The researchers programmed the system so that after the third interruption, the network translates and transcribes the gene for a fluorescing protein, which is visible to researchers.
The second synthetic gene network, called DNA Invertase Cascade (DIC), works in an entirely different way. At the first event, such as the presence of a chemical, the first gene manufactures a protein that cannibalistically snips its own gene out of the network, flips it over and sticks it back in. Once the gene is backwards, it can no longer be transcribed but an extra snippet of DNA the researchers attached to its tail acts as a bookmark, showing protein-making machinery where to resume work. Each successive flip-over counts another event, and the fluorescing protein is activated after the third one.
In both methods, researchers can move the genetic parts in these counters around to fit their needs. The network might be extended to count to higher numbers, or additional genes for fluorescing proteins might be added, for example, to glow red when the bacteria have counted to two, and green at three. The network's counting can be linked to any periodic signal from the outside world the bacteria can detect, or to an internal event, such as a protein only expressed at one point during each cell division.
Each counter has strengths. The RTC can count quickly and works best when events happen every 20 to 30 minutes. The DIC takes longer to execute its flipping action, so works b
|Contact: Ronald Rosenberg|
Boston University Medical Center