Polyamine-mediated phosphorylation of a nucleolar protein from Physarum polycephalum [Fungi] that stimulates rRNA synthesis

• Published in: Proceedings of the National Academy of Sciences - PNAS 1979-06, Vol.76 (6), p.2541-2545
• Main Authors: Kuehn, G.D, Affolter, H.U, Atmar, V.J, Seebeck, T, Gubler, U, Braun, R
• Format: Article
• Language: English
• Subjects: Amino acids; Amino Acids - analysis; Animals; Biological Sciences: Biochemistry; Cell nucleolus; Cell Nucleolus - metabolism; Cellulose nitrate; DNA; DNA Restriction Enzymes; fungi; Gels; Kinetics; Liver Neoplasms, Experimental - metabolism; Molecular Weight; Nucleic Acid Hybridization; Nucleoproteins - metabolism; Phosphoproteins; Phosphoproteins - metabolism; Phosphorylation; Physarum - metabolism; Polyamines; Polyamines - pharmacology; Rats; Ribosomal DNA; RNA; RNA, Ribosomal - biosynthesis; Transcription, Genetic
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.76.6.2541

An acidic nucleolar phosphoprotein with a subunit Mrof 70,000 was purified as an apparent dimer of 139,000 from isolated nuclei of the slime mold Physarum polycephalum. The protein was purified without the aid of strong dissociating agents after its selective phosphorylation in isolated nuclei by a polyamine-mediated reaction. Its amino acid composition resembled that of a nucleolar phosphoprotein from Novikoff hepatoma ascites cells. The phosphoprotein stimulated rRNA synthesis 5-fold by RNA polymerase I within a nucleolar, ribosomal deoxyribonucleoprotein complex isolated from nucleoli of P. polycephalum. It was also identified as a component of the complex. It bound with high affinity and specificity to the palindromic ribosomal DNA of 38 × 106Mrfrom P. polycephalum, which contained two coding sequences for 5.8S, 19S, and 26S rRNA. It also bound to three fragments of ribosomal DNA of Mr21.2 × 106, 17.1 × 106, and 8.1 × 106, prepared by cleavage with restriction endonucleases HindIII, Pst I, and BamHI, respectively. All of these fragments included the symmetry axis of the palindromic ribosomal DNA. The phosphoprotein that had been treated with alkaline phosphatase-agarose to hydrolyze the phosphate groups did not stimulate transcription and did not bind to ribosomal DNA or to the restriction fragments indicated. We have thus isolated a specific phosphoprotein with the capacity to stimulate transcription of a specific set of genes in a eukaryote. These findings suggest that this phosphoprotein may specifically regulate functions of ribosomal DNA in a manner dependent on its degree of phosphorylation.