It has recently become clear that components of the proteasome are recruited to sites of gene transcription. Prevailing evidence suggests that the transcriptionally relevant form of the proteasome is a subcomplex of 19S base proteins, which functions as an ATP-dependent chaperone that influences transcriptional processes. Despite this notion, compelling evidence for a transcription-dedicated 19S base complex is lacking, and 20S proteasome subunits have been shown to associate with chromatin in some contexts. To gain insight into the form of the proteasome that is recruited to chromatin, we assembled a panel of highly specific antibodies that recognize native yeast proteasome subunits in chromatin immunoprecipitation assays. Using these reagents, we show that components from the three major subassemblies of the proteasome-19S lid, 19S base, and 20S core-associate with the activated GAL10 gene in yeast in a virtually indistinguishable manner. We find that proteasome subunits Rpt1, Rpt4, Rpn8, Rpn12, Pre6, and Pre10 are recruited to GAL10 rapidly upon galactose induction. These subunits associate with the entire transcribed portion of GAL10, display near-identical patterns of distribution, and dissociate from chromatin rapidly once transcription is shut down. We also find that proteasome subunits are enriched at telomeres and at genes transcribed by RNA polymerase III. Our data suggest that the transcriptionally relevant form of the proteasome is the canonical 26S complex.T he ubiquitin-proteasome system (UPS) plays a major role in cellular homeostasis by influencing the steady-state levels of proteins involved in processes such as cell cycle control, signaling, protein sorting, and apoptosis. Accumulating evidence suggests that the UPS is also involved in the regulation of gene expression, and that components of the UPS interact with chromatin and act both proteolytically and nonproteolytically to influence transcriptional processes. Perhaps one of the most interesting examples of how the UPS controls transcription centers on the proteasome, which has been linked to events in transcription ranging from control of activators and coactivators through to histone modifications, transcriptional elongation, and repression of cryptic transcription. The widespread involvement of the proteasome in transcription raises the intriguing possibility that it is involved in a majority of the critical steps in gene regulation.Currently, a consensus has yet to emerge on the form of the proteasome that is recruited into transcriptional processes. A popular model posits that it is not the proteasome, but rather a subset of proteasomal ATPases from the 19S base complex, that interacts with chromatin during transcriptional activation. This complex, termed APIS (1), is argued to act independent of the 26S proteasome as a transcriptional chaperone that facilitates protein-protein interactions necessary for transcriptional activation. Support for APIS comes from genetic and biochemical evidence tying 19S base components to transcriptional...