Core DNA replication proteins mediate the initiation, elongation, and Okazaki fragment maturation functions of DNA replication. Although this process is generally conserved in eukaryotes, important differences in the molecular architecture of the DNA replication machine and the function of individual subunits have been reported in various model systems. We have combined genome-wide bioinformatic analyses of Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa) with published experimental data to provide a comprehensive view of the core DNA replication machinery in plants. Many components identified in this analysis have not been studied previously in plant systems, including the GINS (go ichi ni san) complex (PSF1, PSF2, PSF3, and SLD5), MCM8, MCM9, MCM10, NOC3, POLA2, POLA3, POLA4, POLD3, POLD4, and RNASEH2. Our results indicate that the core DNA replication machinery from plants is more similar to vertebrates than single-celled yeasts (Saccharomyces cerevisiae), suggesting that animal models may be more relevant to plant systems. However, we also uncovered some important differences between plants and vertebrate machinery. For example, we did not identify geminin or RNASEH1 genes in plants. Our analyses also indicate that plants may be unique among eukaryotes in that they have multiple copies of numerous core DNA replication genes. This finding raises the question of whether specialized functions have evolved in some cases. This analysis establishes that the core DNA replication machinery is highly conserved across plant species and displays many features in common with other eukaryotes and some characteristics that are unique to plants.DNA replication depends on the coordinated action of numerous multiprotein complexes. At the simplest level, it requires an initiator to establish the site of replication initiation, a helicase to unwind DNA, a polymerase to synthesize new DNA, and machinery to process the Okazaki fragments generated during discontinuous synthesis. Much is known about the DNA replication machinery in yeast (Saccharomyces cerevisiae) and animal model systems, but relatively little is known about the apparatus in plants. To gain insight into plant DNA replication components, we have combined published experimental information with our own bioinformatic analysis of genomic sequence data to examine the core DNA replication machinery in the model plants Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa).Figure 1 depicts a model eukaryotic DNA replication fork and illustrates the protein complexes known or suspected to be part of the core DNA replication machine. These complexes mediate the initiation, elongation, and maturation stages of DNA replication and, as such, constitute the core eukaryotic DNA replication machinery. The events leading to the formation of an active DNA replication fork occur in a stepwise fashion, but our understanding of the timing and specific details of how these events unfold in diverse eukaryotes is limited, and there are a growing number of examples of vari...