Part:BBa_K1075036

AraC-pBAD-RBS32-ccdA-ssrA-TT

The part carries the ssrA-tagged antitoxin ccdA with a ribosomal binding site and a double terminator under the control of the AraC-pBAD promotor system.

CcdA inhibits the toxin ccdB by binding to it and thus represses cell death. The part contains ccdA with a ssrA tag under the control of the ara operon.

Usage and Biology

The ccd module is a toxin-antitoxin (TA) system. The module naturally occurs on the F Plasmid in Escherichia coli bacteria and is essential for their survival. Normally the toxin ccdB is inactivated by the presence of the antitoxin ccdA in the form of a ccdAB complex. If ccdA is no longer available, ccdB inhibits DNA gyrase which leads to cell death. Gyrase is a type IIA topoisomerase specific to E. coli and is able to produce negative DNA supercoiling by making a double-strand break in the DNA and religating it. CcdB stabilizes the gyrase cleavage complex and thus blocks the catalytic function of the gyrase. That means that the gyrase remains bound to the DNA and the cleaved DNA is not religated. DNA- and RNA polymerases can’t copy the DNA anymore and cell proliferation as well as protein biosynthesis is stopped. The double-stranded breaks in the DNA initiate cell death. [http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1635281/][http://www.ncbi.nlm.nih.gov/pubmed/?term=A+Common+Origin+for+the+Bacterial+Toxin-Antitoxin+Systems+parD+and+ccd]