beta-strand (B) domain of GINS complex proteins: Sld5, Psf1, Psf2, Psf3, Gins51 and Gins23The GINS (named from the Japanese go-ichi-ni-san, meaning 5-1-2-3 for the Sld5, Psf1, Psf2, and Psf3 subunits) complex is involved in both the initiation and elongation stages of eukaryotic chromosome replication, with GINS being the component that most likely serves as the replicative helicase that unwinds duplex DNA ahead of the moving replication fork. This complex is found in eukaryotes and archaea, but not in bacteria. In eukaryotes, GINS is a tetrameric arrangement of four subunits Sld5, Psf1, Psf2 and Psf3, while in archaea, it consists of two different proteins named Gins51 and Gins23. The archaeal GINS complex can be either an alpha2beta2-type heterotetramer composed of Gins51 and Gins23, or a Gins51-only alpha4-type homotetramer. All GINS subunits are homologous and consist of two domains, called the alpha-helical (A) and beta-strand (B) domains. The A and B domains of Sld5/Psf1/Gins51 are permuted with respect to Psf1/Psf3/Gins23. The overall tetrameric assemblies of GINS are similar, but the relative locations of the C-terminal small domains are different with respect to the alpha-helical domain, resulting in different subunit contacts. However, the basic function of GINS in DNA replication is conserved across eukaryotes and archaea. This model represents the beta-strand domain (B-domain) of GINS complex proteins.