Charged Residues Flanking the Transmembrane Domain of Two Related Toxin-Antitoxin System Toxins Affect Host Response.

A majority of toxins produced by type I toxin-antitoxin (TA-1) systems are small membrane-localized proteins that were initially proposed to kill cells by forming non-specific pores in the cytoplasmic membrane. The examination of the effects of numerous TA-1 systems indicates that this is not the mechanism of action of many of these proteins. produces two toxins of the Fst/Ldr family, one encoded on pheromone-responsive conjugative plasmids (Fst) and the other on the chromosome, Fst. Previous results demonstrated that overexpression of the toxins produced a differential transcriptomic response in cells. In this report, we identify the specific amino acid differences between the two toxins responsible for the differential response of a gene highly induced by Fst but not Fst. In addition, we demonstrate that a transporter protein that is genetically linked to the chromosomal version of the TA-1 system functions to limit the toxicity of the protein.