Phosphorylation of Bacillus subtilis gene regulator AbrB modulates its DNA-binding properties

AbrB is a global gene regulator involved in transition phase phenomena in Bacillus subtilis. It participates in a complex regulatory network governing the expression of stationary phase functions. AbrB was previously found to be phosphorylated on serine 86 located close to its C-terminal oligomerization domain. Here we report that AbrB can be phosphorylated by three B. subtilis serine/threonine kinases expressed during the transition and stationary phase: PrkC, PrkD and YabT. Our in vitro findings suggest that AbrB phosphorylation impedes its DNA binding and abolishes binding cooperativity. In vivo we established that a phospho-mimetic mutation abrB S86D leads to a significant loss of AbrB control over several key target functions: exoprotease production, competence development and sporulation. A wider transcriptome analysis of abrB S86D and S86A mutant strains revealed deregulation of a large number of target genes. We therefore propose that AbrB phosphorylation serves as an additional input for fine-tuning the activity of this ambiactive gene regulator. A 6 arrays study of the transcriptome profiles of B. subtilis strain 168, abrB-S86A and abrB-S86D mutant strains. Compared to the wild-type strain the mutant strains were used to test the effect of the phosphorylation of AbrB on ser-86 (using a phosphomimetic of AbrB (abrB-S86D strain) or its absence (abrB-S86A strain) on transcript profiles.