The GINS complex is composed of four subunits, encoded by SLD5, PSF1, PSF2, and PSF3. In S. cerevisiae, it was first identified by genetic and biochemical methods to determine factors interacting with Sld5p. Genetic interactions between these four genes also suggest that they act together. The GINS complex was independently isolated in a large scale screen for cell cycle defects. A similar complex is found in Xenopus and has a ring-like structure. In yeast, all four genes are essential and cells defective in SLD5, PSF1, or PSF2 are impaired in their ability to replicate DNA. The complex localizes to origins of DNA replication and Sld5p was previously implicated as functioning in DNA replication due to its genetic interaction with DPB11. Additional genetic and biochemical interactions of the GINS complex with Dpb11p, Dpb2p, and Sld3p suggest that it functions in some way at the replication fork during DNA synthesis.