STRUCTURE OF THE ESCHERICHIA-COLI RNA-POLYMERASE ALPHA-SUBUNIT AMINO-TERMINAL DOMAIN

The 2.5 angstrom resolution x-ray crystal structure of the Escherichia coil RNA polymerase (RNAP) alpha subunit amino-terminal domain (alpha NTD), which is necessary and sufficient to dimerize and assemble the other RNAP subunits into a transcriptionally active enzyme and contain s all of the sequence elements conserved among eukaryotic alpha homolo gs, has been determined. The alpha NTD monomer comprises two distinct, flexibly linked domains, only one of which participates in the dimer interface. In the alpha NTD dimer, a pair of helices from one monomer interact with the cognate helices of the other to form an extensive hy drophobic core. ALL of the determinants for interactions with the othe r RNAP subunits lie on one face of the aNTD dimer. Sequence alignments , combined with secondary-structure predictions, support proposals tha t a heterodimer of the eukaryotic RNAP subunits related to Saccharomyc es cerevisiae Rpb3 and Rpb11 plays the role of the alpha NTD dimer in prokaryotic RNAP.