Investigations on the mechanism of heat-induced programmed cell death mediated by a MazE-MazF like type ll toxin-antitoxin system in the cyanobacterium, synechocystis sp. PCC 6803

Abstract

TA systems have been identified as small genetic elements, generally organised as a dicistronic operon, consisting of an antitoxin gene preceeding the toxin gene in most of the cases and have been reported to be present in bacteria as well as in archaea. These genes encode a stable toxin and a comparatively labile or less stable antitoxin, which can either be a protein or RNA. The antitoxin binds to the toxin, forming a TA complex where it neutralizes the function of the toxin (Gerdes et al, 2005). Being labile, in order to neutralize the toxin, the antitoxin has to be continuously expressed in the cell, but under various stress conditions the antitoxin has been reported to be degraded by proteolysis and / or regulated at its transcription level (Christensen et al, 2001, 2003; Vogel et al, 2004). This change in the levels of the antitoxin, frees the toxin from the TA complex and the free toxin thus exerts its inhibitory effect on various essential cellular metabolic pathways, ultimately leading to the death of the cell or causing a bacterial growth arrest (Figure 1.1).