DNA replication, the process where the genetic material is duplicated, is one of the most important and basic processes a cell undertakes. It is essential that this process is tightly and carefully regulated as errors in DNA replication are catastrophic, resulting in diseases like cancer. The synthetic or S phase of the eukaryotic cell cycle is entirely devoted to genome duplication by orchestrating two processes: DNA replication and histone production. Histones are small basic proteins that together with the DNA form the nucleosome, the repetitive subunit of chromatin. Nucleosomes provide for save storage of linear DNA and contribute to genome integrity. However, nucleosomes are very stable which limits the access of underlying DNA and thus has inhibitory effects on DNA replication, gene expression and DNA repair. Although tremendous progress has been made in order to reveal the molecular mechanisms, clear gaps remain in our understanding of DNA replication biology. One of these important questions is how the replication machinery overcomes the chromatin barrier for efficient DNA duplication. The goal of this proposal is to shed light onto how DNA replication initiates and the replisome elongates on chromatin.