The 19S regulatory particle of the proteasome is required for efficient transcription elongation by RNA polymerase II

It is generally thought that the primary or even sole activity of the 19S r egulatory particle of the 26S proteasome is to facilitate the degradation o f polyubiquitinated proteins by the 20S-core subunit. However, we present e vidence that the 19S complex is required for efficient elongation of RNA po lymerase II (RNAP II) in vitro and in vivo. First, yeast strains carrying a lleles of SUGI and SUG2, encoding 19S components, exhibit phenotypes indica tive of elongation defects. Second, in vitro transcription is inhibited by antibodies raised against Sug1, or by heat-inactivating temperature-sensiti ve Sug1 mutants with restoration of elongation by addition of immunopurifie d 19S complex. Finally, Cdc68, a known elongation factor, coimmunoprecipita tes with the 19S complex, indicating a physical interaction. Inhibition of the 20S proteolytic core of the proteasome has no effect on elongation. Thi s work defines a nonproteolytic role for the 19S complex in RNAP II transcr iption.