Solution structure of the RNA polymerase subunit RPB5 from Methanobacterium thermoautotrophicum

RPB5 is an essential subunit of eukaryotic and archaeal RNA polymerases. It is a proposed target for transcription activator proteins in eukaryotes, b ut the mechanism of interaction is not known. We have determined the soluti on structure of the RPB5 subunit from the thermophilic archeon, Methanobact erium thermoautotrophicum. MtRBP5 contains a four-stranded beta-sheet platf orm supporting two rw-helices, one on each side of the beta-sheet, resultin g in an overall mushroom shape that does not appear to have any structural homologues in the structural database. The position and conservation of cha rged surface residues suggests possible modes of interaction with other pro teins, as well as a rationale for the thermal stability of this protein.