In vitro assembly of an archaeal D-L-N RNA polymerase subunit complex reveals a eukaryote-like structural arrangement.

Archaeal RNA polymerases (RNAPs) resemble the eukaryotic nuclear RNAPs in complexity, and many of their subunits display a high degree of sequence similarity to their eukaryotic counterparts. Here we describe specific protein-protein contacts present between individual recombinant RNAP subunits from the archaeon Methanococcus jannaschii. Subunits D and L interact specifically with each other in two-hybrid assays. D also interacts under the same conditions with the RPB11 and AC19 subunits from the yeast Saccharomyces cerevisiae, suggesting that essential elements of the binding surface between these proteins have been conserved across the archaeal/eukaryotic evolutionary domain boundary. Interactions between L and RPB3 or AC40 were, however, not detectable. Recombinant D and L subunits associate under in vitro conditions and copurify with each other during size-exclusion chromatography. Addition of an another recombinant subunit (N) to the D-L complex results in the formation of a triple complex. This D-L-N complex resembles the RPB3-RPB11-RPB10 or AC40-AC19-RPB10 complexes in eukaryotic RNAPIIand RNAPI/RNAPIII, respectively. Our data provide evidence for a close similarity in the quaternary arrangement of a subset of archaeal and eukaryotic RNA polymerase subunits and the conservation of the protein-protein contacts formed between them.