Histone post-translational modifications in DNA damage response

The fact that eukaryotic DNA is packed into chromatin constitutes a physical barrier to enzymes and regulatory factors to reach the DNA molecule for replication, transcription, recombination and repair. Although most studies in this field have concentrated on how chromatin regulates transcription, there is a recent emphasis on studying the role of chromatin in the response to DNA damage. Two main chromatin-remodeling mechanisms have been identified, namely, ATP-dependent chromatin-remodeling complexes and histone post-translational modifications (PTMs). PTMs constitute reversible covalent modifications in aminoacidic residues, such as serine and threonine phosphorylation, lysine acetylation, lysine and arginine methylation and lysine ubiquitylation, among others. Moreover, nucleosome composition can be modified by the incorporation of histone variants, which are assembled into nucleosomes independently of DNA replication. The phosphorylation of the histone variant H2AX (gammaH2AX) is one of the best examples of histone PTMs in response to DNA damage induction, but many others have recently been revealed. In this review, we focus on and summarize the best-known histone PTMs observed in excision repair (base excision and nucleotide excision) and double-strand break (non-homologous end-joining and homologous recombination) repair pathways. In brief, the interplay between chromatin remodelers and DNA repair factors is discussed in relation to DNA damage response mechanisms.