More than just activity control: phosphorylation may control all aspects of a protein's properties.

Protein phosphorylation is a major post-translational modification of proteins. Due to the introduction of a very large, strongly charged group, phosphorylation often has a dramatic effect on the characteristics of the protein, including alterations in activity or interaction properties. In this issue of Molecular Microbiology, Jers et al. have addressed the effect of protein tyrosine phosphorylation in Bacillus subtilis. They demonstrate that tyrosine phosphorylation stimulates the activity of several but not all targets. In addition, the subcellular localization of several proteins was shown to depend on tyrosine phosphorylation that is catalysed by the BY kinase PtkA. This is the first report showing that phosphorylation controls protein localization in bacteria and adds another important function to this post-translational modification.