New insights into the GINS complex explain the controversy between existing structural models.

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• The GINS complex (Growth, INterphase, S-phase) is essential for eukaryotic DNA replication.
• It forms a core component of the replicative fork, facilitating DNA unwinding.
• Previous structural studies using crystallography and electron microscopy (EM) presented conflicting data on GINS complex conformation.

Purpose of the Study:

• To resolve discrepancies between crystallographic and EM data regarding GINS complex structure.
• To investigate the solution structure of the GINS complex and its potential assembly intermediates.
• To understand the role of specific subunits, like the Psf1 subunit's B domain, in GINS complex function.

Main Methods:

• Solution state analysis using electron microscopy (EM).
• X-ray crystallography for high-resolution structural data.
• Small-angle X-ray scattering (SAXS) to study solution structure and dynamics.
• Computational modeling to reconstruct complex structures.

Main Results:

• GINS exists as a compact tetramer in solution, consistent with crystal structures.
• A distinct double-tetrameric population of GINS was identified by EM.
• The B domain of the Psf1 subunit was localized within the free GINS complex, a finding not previously observed.
• The double-tetrameric form is proposed as an intermediate in the assembly of replication machinery.

Conclusions:

• The GINS complex exhibits structural plasticity, existing as both tetrameric and double-tetrameric forms.
• The double-tetramer represents a potential intermediate for the coordinated assembly of two replicative helicases at replication origins.
• Localization of the Psf1 B domain is critical for understanding GINS complex assembly and function in establishing a functional replication fork.