In Saccharomyces cerevisiae, acetylation of lysine 56 (Lys-56) in the globular domain of histone H3 plays an important role in response to genotoxic agents that interfere with DNA replication. However, the regulation and biological function of this modification are poorly defined in other eukaryotes. Here we show that Lys-56 acetylation in Schizosaccharomyces pombe occurs transiently during passage through S-phase and is normally removed in G(2). Genotoxic agents that cause DNA double strand breaks during replication elicit a delay in deacetylation of histone H3 Lys-56. In addition, mutant cells that cannot acetylate Lys-56 are acutely sensitive to genotoxic agents that block DNA replication. Moreover, we show that Spbc342.06cp, a previously uncharacterized open reading frame, encodes the functional homolog of S. cerevisiae Rtt109, and that this protein acetylates H3 Lys-56 both in vitro and in vivo. Altogether, our results indicate that both the regulation of histone H3 Lys-56 acetylation by its histone acetyltransferase and histone deacetylase and its role in the DNA damage response are conserved among two distantly related yeast model organisms.