1.C.64 The Fst Toxin (Fst) Family
The Fst toxin is a 33 amino acid peptide toxin encoded by a stable RNAI message of the partition (par) toxin-antitoxin stability determinant of the Enterococcus faecalis conjugative plasmid, pAD1 (Weaver et al., 2003). It shows no significant sequence similarity to other proteins in the NCBI database (4/03). Intracellular production of Fst inhibits macromolecular synthesis, inhibits cell growth, and renders the cell permeable to the DNA stain, Sytox Green, which cannot normally pass through the membrane. Fst increased the number of cells stained at least 10-fold, but did not allow nutrient efflux. It may allow selective pore formation. It functions synergistically with nisin, a lantibiotic pore former (see TC #1.C.30.1.1). Mutants resistant to Fst have altered membrane composition (Weaver et al., 2003).