The Expanding Landscape of ADP-Ribosylation: Protein, DNA, RNA, and Mitochondrial Regulation

ADP-ribosylation is an essential post-translational modification that contributes to key cellular processes, such as DNA damage repair, cell-cycle progression, chromatin remodeling, mitochondrial function, and immune responses in mammalian cells. This modification derives from NAD⁺ and is regulated by dedicated writer, eraser, and reader proteins that govern its installation, removal, and recognition. Traditionally viewed as a protein-centered modification, ADP-ribosylation has recently been extended to nucleic acids, with ADP-ribosylated DNA and RNA now identified in both mammalian and bacterial systems. These discoveries reveal previously underappreciated layers of nucleic acid-based regulation and suggest that NAD⁺-dependent chemistry integrates genome maintenance, RNA metabolism, and cellular stress responses. In this review, we first outline the major mammalian ADP-ribosylation machineries, including the families of writer, eraser, and reader proteins, and discuss how their activities are coordinated. We then examine emerging roles of ADP-ribosylation in mitochondria, with a focus on mitochondrial DNA repair and metabolic control. Finally, we highlight recent advances in understanding NAD⁺-dependent modifications of DNA and RNA in mammalian and bacterial cells, including terminal and nucleobase-linked ADP-ribosylation and NAD capping, and discuss outstanding questions regarding their physiological functions and interplay with protein post-translational modification and other nucleic acid modifications.