FIG 2.

Overview of bacterial epigenetics. (a) There are two broad classes of bacterial DNA modifications: methylation of adenines and cytosines and phosphorothioation of the DNA backbone, where a nonbridging oxygen gets replaced by sulfur. Bacterial DNA methylation is mediated by enzymes belonging to the restriction-modification (R-M) systems or orphan methyltransferases. Phosphorothioation is facilitated by the gene products of a DNA degradation (DND) system, dndABCDE. (b) Two classes of epigenetic modifications of bacterial mRNA have been discovered: methylation of adenine at N⁶ and NAD capping at the 5′ end.