Structure-function relationship and regulation of two Bacillus subtilis DNA-binding proteins, HBsu and AbrB

Microorganisms use a number of small basic proteins for organization and compaction of their DNA. By their interaction with the genome, these proteins do have a profound effect on gene expression, growth behavior, and viability. It has to be distinguished between indirect effects as a consequence of the state of chromosome condensation and relaxation that influence the rate of RNA polymerase action as represented by the histone-like proteins, and direct effects by specific binding of proteins to defined DNA segments predominantly located around promoter sequences. This latter class is represented by the transition-state regulators that are involved in integrating various global stimuli and orchestrating expression of the genes under their regulation for a better adaptation to changes in growth rate. In this article we will focus on two different but abundant DNA binding proteins of the gram-positive model organism Bacillus subtilis, the histone-like HBsu as a member of the unspecific and the transition state regulator AbrB as a member of specific classes of DNA binding proteins.