Clocks and switches:: bacterial gene regulation by DNA adenine methylation

N-6 methylation in adenosine moieties causes changes in DNA structure and can modulate DNA-protein interactions. In both alpha-Proteobacteria and gamma- Proteobacteria, postreplicative formation of N-6-methyl-adenine regulates transcription of specific genes and provides two general types of controls: (i) clock-like controls that permit transient gene transcription during a specific stage of DNA replication; (ii) switch-like controls in which transcription is regulated by a DNA methylation pattern. DNA adenine methylation may also regulate gene expression by affecting nucleoid topology. Recent transcriptomic studies have unveiled novel cases of genes regulated by DNA adenine methylation, including virulence genes of bacterial pathogens.