RNA contacts the two large polymerase subunits and a 52-kDa polypeptide in nucleolar RNA polymerase I transcribing complexes.
The interactions between nascent RNA and RNA polymerase I-transcribing complexes were studied by photoaffinity labeling in HeLa nucleoli. Specific labeling of enzyme subunits Ia, Ib, and of a 52-kDa polypeptide was observed. The 52-kDa polypeptide was shown to be associated with the transcribing complex by immunoprecipitation with RNA polymerase I antibodies and by glycerol gradient centrifugation. Transcripts that were kept short by inclusion of a chain-terminating nucleotide or with short incubation times contacted mainly subunits Ia and Ib. Decreasing chain terminator concentration or increasing incubation time resulted in additional labeling of the 52-kDa polypeptide. These data indicate that the 52-kDa polypeptide contacts nascent RNA after it has left the Ia-Ib domain.
Roberge
M
M
Department of Biological Chemistry, School of Medicine, University of California, Davis 95616.
Bradbury
E M
EM
D002466:Cell Nucleolus / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D006367:HeLa Cells / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight; D012318:RNA Polymerase I / Q000302:isolation & purification / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism / Q000648:ultrastructure; D014158:Transcription, Genetic
D046911:Macromolecular Substances; D012318:RNA Polymerase I