Identification of a novel cell division protein in Bacillus subtilis

Abstract

FtsZ is a tubulin-like protein that polymerizes into a ring like structure at midcell, which is the first step in septum formation. The dynamics of FtsZ polymerization is regulated by a set of proteins, one of which is ZapA. ZapA is a non-essential positive regulator of FtsZ polymerization. In this study we have performed a screen for mutations in Bacillus subtilis that result in a cell division defect when combined with ΔzapA. Three such mutations were found in the yvcL gene. Since this gene is homologous to whiA from Streptomyces coelicolor, and the lack of both proteins imposes in some instances similar phenotypes, we proposed to rename the gene whiA. Mutation of whiA alone had only a mild effect on cells, which became 20-60% longer. However, the double mutant ΔwhiA ΔzapA is filamentous and sick. Evidence is provided that the filamentation is caused by delocalization of FtsZ, and that WhiA is implemented in the early stage of cell division. Interestingly, WhiA localizes to the nucleoid and is important in cells that overinitiate replication. We also found that this protein is essential for survival after UV-induced DNA damage. Its binding sites on DNA were identified using a ChIP-on-chip method and the dif site, which is important for chromosome dimer resolution, was found to be a possible target of WhiA. A transcriptome analysis using whole genome microarray showed that WhiA does not function as transcriptional regulator. We conclude that WhiA is involved in both cell division and chromosome dynamics.