Functions as part of the GINS complex which plays an essential role in the initiation of DNA replication by binding to DNA replication origins and facilitating the assembly of the DNA replication machinery. Component of the GINS complex which is a heterotetramer of SLD5, PSF1, PSF2 and PSF3. Interacts with PSF1 and SLD5. Belongs to the GINS2/PSF2 family.