title: In vitro evidence that eukaryotic ribosomal RNA transcription is regulated by modification of RNA polymerase I.
abstract: We have utilized a cell-free transcription system from Acanthamoeba castellanii to test the functional activity of RNA polymerase I and transcription initiation factor I (TIF-I) during developmental down regulation of rRNA transcription. The results strongly suggest that rRNA transcription is regulated by modification, probably covalent, of RNA polymerase I: (1) The level of activity of TIF-I in extracts from transcriptionally active and inactive cells is constant. (2) The number of RNA polymerase I molecules in transcriptionally active and inactive cells is also constant. (3) In contrast, though the specific activity of polymerase I on damaged templates remains constant, both crude and purified polymerase I from inactive cells have lost the ability to participate in faithful initiation of rRNA transcription. (4) Polymerase I purified from transcriptionally active cells has the same subunit architecture as enzyme from inactive cells. However, the latter is heat denatured 5 times faster than the active polymerase.
mesh_terms: D000656:Amoeba / Q000235:genetics* / Q000254:growth & development; D000818:Animals; D004262:DNA Restriction Enzymes; D004275:DNA, Ribosomal / Q000235:genetics*; D007700:Kinetics; D012318:RNA Polymerase I / Q000302:isolation & purification / Q000378:metabolism*; D012335:RNA, Ribosomal / Q000235:genetics*; D013816:Thermodynamics; D014158:Transcription, Genetic
chemical_list: D004275:DNA, Ribosomal; D012335:RNA, Ribosomal; D012318:RNA Polymerase I; D004262:DNA Restriction Enzymes