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.