Clocks and switches: bacterial gene regulation by DNA adenine methylation

N6 methylation in adenosine moieties causes changes in DNA structure and can modulate DNA–protein interactions. In both α-Proteobacteria and γ-Proteobacteria, postreplicative formation of N6-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.