RNA Polymerase    DNA-directed RNA polymerase catalyzes the synthesis of RNA on a DNA template. The core enzyme has three polypeptide subunits: alpha, beta, & beta' in a stoichiometry of α2ββ' & an additional subunit, omega.  Core RNA polymerase can bind to DNA and catalyze the synthesis of RNA, but has no specificity, it needs a 5th subunit sigma factor to make it the holoenzyme.

   alpha -
α - required for assembly of the enzyme;
                 interacts with some regulatory proteins;
                  also involved in catalysis

   betaβ - involved in catalysis: chain initiation and elongation

   beta prime - β' - binds to the DNA template

   sigma - σ - directs enzyme to a promoter, initiates transcription

   omega - ω - required to restore denatured RNA polymerase
                     in vitro to its fully functional form