Subunit contacts in the Thermococcus kodakaraensis and human GINS complexes. Close-up views of the upper-lower layer subunit contacts, shown by stereo pairs. The conserved intermolecular helix-helix contacts observed in the first area are indicated by red arrows, and those unique in each upper-lower subunit pair in the second area are indicated by blue arrows. The conserved tryptophan residues are depicted by stick models. (A) T. kodakaraensis Gins51-Gins23. (B) Human Sld5-Psf2 and (C) Psf1-Psf3. (D) Schematic drawing of the subunit contacts.