The two eukaryotic subunits Rpb3 and Rpb11 dimerize to from a platform onto which the other subunits of the RNA polymerase assemble (D/L in archaea). The prokaryotic equivalent of the Rpb3/Rpb11 platform is the alpha-alpha dimer. The dimerization domain of the alpha subunit/Rpb3 is interrupted by an insert domain (pfam01000). Some of the alpha subunits also contain iron-sulphur binding domains (pfam00037). Rpb11 is found as a continuous domain. Members of this family include: alpha subunit from eubacteria, alpha subunits from chloroplasts, Rpb3 subunits from eukaryotes, Rpb11 subunits from eukaryotes, RpoD subunits from archaeal spp, and RpoL subunits from archaeal spp. Many of the members of this family carry only the N-terminal region of Rpb11.