In vitro characterization of the type I toxin-antitoxin system bsrE/SR5 from Bacillus subtilis [Gene Regulation]

November 12th, 2015 by Meissner, C., Jahn, N., Brantl, S.

BsrE/SR5 is a new type I toxin/antitoxin system located on the prophage-like region P6 of the B. subtilis chromosome. The bsrE gene encoding a 30 amino acid hydrophobic toxin and the antitoxin gene sr5 overlap at their 3` ends by 112 bp. Overexpression of bsrE causes cell lysis on agar plates. The presence of sr5 ensures a growth advantage of B. subtilis cells. Here, we present a detailed in vitro analysis of bsrE/SR5. The secondary structures of SR5, bsrE mRNA and the SR5/bsrE RNA complex were determined. Apparent binding rate constants (kapp) of wild-type and mutated SR5 species with wild-type bsrE mRNA were calculated and SR5 regions required for efficient inhibition of bsrE mRNA narrowed down. In vivo studies confirmed the in vitro data but indicated that a so far unknown RNA binding protein might exist in B. subtilis that can promote antitoxin/toxin RNA interaction. Using time course experiments, the binding pathway of SR5 and bsrE RNA was elucidated. A comparison with the previously well-characterized type I TA system from the B. subtilis chromosome, bsrG/SR4, reveals similarities, but also significant differences.