title: Phosphorylation of RNA polymerase I-associated polypeptides of Tetrahymena pyriformis.
abstract: In the ciliate Tetrahymena pyriformis phosphorylation of RNA polymerase I [EC 2.7.7.6] and of polymerase-associated polypeptides was investigated in growing and growth-arrested cultures which differ widely in their rates of rRNA synthesis. Several putative subunits of RNA polymerase I (of 180, 21.5, and 19.5 kDa) and a polymerase-associated polypeptide of 27 kDa were found to be phosphorylated, independent of the growth conditions. However, an additional enzyme-associated polypeptide of 26 kDa was intensively labeled with 32P only after arrestment of growth by starvation. The molar quantities of both phosphorylated, enzyme-associated polypeptides thereby did not differ in growing and growth-arrested cultures, and the specific 32P-labeling of cellular ATP remained nearly unchanged under the different culture conditions. These findings indicate a selective, reversible phosphorylation of the RNA polymerase I-associated 26 kDa polypeptide correlated with conditions of repressed rRNA synthesis induced by the starvation procedure. In vitro phosphorylation in macronuclei isolated from growing and growth-arrested cultures using [gamma-32P]ATP revealed essentially the same pattern of labeling of the enzyme-associated polypeptides of 27 and 26 kDa as it was found in vivo.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D002499:Centrifugation, Density Gradient; D010455:Peptides / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D012318:RNA Polymerase I / Q000378:metabolism*; D013769:Tetrahymena pyriformis / Q000201:enzymology* / Q000254:growth & development / Q000378:metabolism
chemical_list: D010455:Peptides; D000255:Adenosine Triphosphate; D012318:RNA Polymerase I