In eukaryotes, chromatin structure and topology have profound influence on DNA metabolic processes such as DNA replication, transcription, and DNA damage repair. These processes are regulated by histone modifications and modifiers including histone acetylation and regulators of histone acetylation. However, how transcription influences replication fork stability and the mechanisms that has evolved to navigate through transcription and replication interactions, when these processes should occur simultaneously in eukaryotic cells in chromatin context, are not well understood. Highly conserved Sirtuins family histone deacetylases play crucial roles in various cellular processes including cell survival, transcription and genome stability by deacetylating histones and non-histone proteins. We have earlier reported that deletion of hst4 (a sir2 homolog in fission yeast) results in S-phase delay and reduced BrdU incorporation indicating defect in DNA replication. To study the mechanism in detail, we assessed BrdU incorporation to measure global replication rate using flow cytometry and observed a delay in S- phase entry and defect in the rate of replication upon hst4 deletion in S. pombe. The only known substrate of Hst4 is histone H3K56 acetylation. It has recently shown that H3K56 acetylation sensitizes cells to replicative stress in part by negatively regulating DNA replication origin activation. DNA replication dynamics is known to depend on replication origin firing and fork progression. Hence, we checked the role of hst4 on origin firing using BrdU-IP followed by semi-quantitative PCR at few origins and observed early origin to be less active at the mid-S phase in hst4 deficient strain, indicating the role of hst4 in defining the replication origin firing pattern. BrdU-IP-Sequencing to map the genome-wide origin firing pattern shows overall replication efficiency is compromised regardless of early and late origins in upon hst4 deletion. Interestingly, there are few exceptions to this where BrdU incorporation has increased in the mutant which could partially be due to firing of dormant origins due to hyper-acetylation. Further analysis in progress that indicated alteration in replication associated domains which correlates with the topologically associated domains in the mutant. We are also studying how increase in transcription due to this hyperacetylation influence interaction between DNA replication and transcription. Knowledge from this study is expected to extrapolate to the human system and can be used in designing therapeutics against pathophysiology.