DNA polymerase δ (Pol δ) from Saccharomyces cerevisiae consists of three subunits, Pol3 (125 kDa), Pol31 (55 kDa), and Pol32 (40 kDa), present at a 1:1:1 stoichiometry in purified preparations. Previously, based on gel filtration studies of Pol δ, we suggested that the enzyme may be a dimer of catalytic cores, with dimerization mediated by the Pol32 subunit (Burgers, P. M., and Gerik, K. J. (1998) J. Biol. Chem. 273, 19756-19762). We now report on extensive gel filtration, glycerol gradient sedimentation, and analytical equilibrium centrifugation studies of Pol δ and of several subassemblies of Pol δ. The hydrodynamic parameters of these assemblies indicate that (i) Pol32 is a rod-shaped protein with a frictional ratio f/f o = 2.22; (ii) any complex containing Pol32 also has an extremely asymmetric shape; (iii) the results of these studies are independent of concentration (varied between 0.1-20 μM); (iv) all complexes are monomeric under the conditions studied (up to 20 μM). Moreover, a two-hybrid analysis of the Pol32 subunit did not detect a Pol32-Pol32 interaction in vivo. Therefore, we conclude that the assembly structure of Pol δ is that of a monomer.