Psf1 is a component of the GINS tetrameric protein complex. Psf1 is mainly expressed in highly proliferative tissues, such as blastocysts, adult bone marrow, and testis, in which the stem cell system is active. Loss of Psf1 causes embryonic lethality. GINS is a complex of four subunits (Sld5, Psf1, Psf2 and Psf3) that is involved in both initiation and elongation stages of eukaryotic chromosome replication. Besides being essential for the maintenance of genomic integrity, GINS plays a central role in coordinating DNA replication with cell cycle checkpoints and is involved in cell growth. The eukaryotic GINS subunits are homologous and homologs are also found in the archaea; the complex is not found in bacteria. The four subunits of the complex consist of two domains each, termed the alpha-helical (A) and beta-strand (B) domains. The A and B domains of Sld5/Psf1 are permuted with respect to Psf1/Psf3.
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