ShoB pore-forming toxin, also called RyfB or YphI, of 26 aas with 1 TMS. More is known about how their expression is regulated than their biological function. Although all are found in  E. coli and closely related bacteria, there is great variation among species as to which loci they possess. Fozo 2012 discussed how these sRNA antitoxins prevent toxin production and how the distribution of these loci across species may be providing insights into their true function. Overexpression causes cessation of growth and rapid membrane depolarization. Overexpression induces the stress-response and the induction of a number of membrane protein-encoding genes (Fozo et al. 2008).