Elongator, a multisubunit component of a novel RNA polymerase II holoenzyme for transcriptional elongation

The form of RNA polymerase II (RNAPII) engaged in transcriptional elongatio n was isolated. Elongating RNAPII was associated with a novel multisubunit complex, termed elongator, whose stable interaction was dependent on a hype rphosphorylated state of the RNAPII carboxy-terminal domain (CTD). A free f orm of elongator was also isolated, demonstrating the discrete nature of th e complex, and free elongator could bind directly to RNAPII. The gene encod ing the largest subunit of elongator, ELP1, was cloned. Phenotypes of yeast elp1 Delta cells demonstrated an involvement of elongator in transcription al elongation as well as activation in vivo. Our data indicate that the tra nsition from transcriptional initiation to elongation involves an exchange of the multiprotein mediator complex for elongator in a reaction coupled to CTD hyperphosphorylation.