Eukaryotic DNA replication requires the coordinated activity of the
multi-subunit DNA polymerases: Pol alpha, Pol delta and Pol epsilon. The
conserved catalytic and regulatory B subunits associate in a constitutive
heterodimer that represents the functional core of all three replicative
polymerases. Here, we combine X-ray crystallography and electron microscopy (EM)
to describe subunit interaction and 3D architecture of heterodimeric yeast Pol
alpha. The crystal structure of the C-terminal domain (CTD) of the catalytic
subunit bound to the B subunit illustrates a conserved mechanism of accessory
factor recruitment by replicative polymerases. The EM reconstructions of Pol
alpha reveal a bilobal shape with separate catalytic and regulatory modules.
Docking of the B-CTD complex in the EM reconstruction shows that the B subunit
is tethered to the polymerase domain through a structured but flexible linker.
Our combined findings provide a structural template for the common functional
architecture of the three major replicative DNA polymerases.
