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.