The structure and interactions of SpoIISA and SpoIISB, a toxin-antitoxin system in Bacillus subtilis.

Spore formation in Bacillus subtilis begins with an asymmetric cell division, following which differential gene expression is established by alternative compartment-specific RNA polymerase σ factors. The spoIISAB operon of B. subtilis was identified as a locus whose mutation leads to increased activity of the first sporulation-specific sigma factor, σ(F).

Expression of functional Bacillus SpoIISAB toxin-antitoxin modules in Escherichia coli.

SpoIISA and SpoIISB proteins from Bacillus subtilis belong to a recently described bacterial programmed-cell death system. The current work demonstrates that the toxin-antitoxin module is also functional in Escherichia coli cells, where the expression of SpoIISA toxin leads to transient growth arrest coupled with cell lysis, and SpoIISA-induced death can be prevented by coexpression of its cognate antitoxin, SpoIISB. Escherichia coli cells appear to be able to escape the SpoIISA killing by activation of a specific, as yet unidentified protease that cleaves out the cytosolic part of the protein.

Conformation families of protein fragments in multidimensional torsion-angle space.

Protein conformation families for automatic model building were determined for dipeptidic, tripeptidic, tetrapeptidic and pentapeptidic fragments. Mapping in n-dimensional conformational space (n = 2, 4 and 6), a conformation-generator method, a deletion-sorting process and a verification procedure were used to calculate the conformational preferences. Torsion angles were harvested from PDB structures with resolutions better than 1.