Required for correct functioning of the GINS complex, a complex that plays an essential role in the initiation of DNA replication, and progression of DNA replication forks (PubMed:12730133). GINS complex seems to bind preferentially to single-stranded DNA (By similarity). Component of the GINS complex which is a heterotetramer of gins1/psf1, gins2/psf2, gins3/psf3 and gins4/sld5 (PubMed:12730133). Component of the CMG helicase complex, composed of the mcm2-7 complex, the GINS complex and cdc45 (PubMed:30979826, PubMed:30842657). Associates with chromatin. Belongs to the GINS1/PSF1 family.