Mrp family proteins are ATPases with a variety of functions. Bacillus subtilis protein‐tyrosine kinase PtkA phosphorylates the Mrp protein SalA. Phosphorylated SalA represses scoC which encodes a repressor of aprE , encoding a major exoprotease. SalA and PtkA contain the same ATP‐binding Walker domain, and have thus presumably arose from a common ancestor. For details, see the article by Derouiche et al . on pp. 1195–1208 of this issue.