title: A ribonuclease from yeast associated with the 40 S ribosomal subunit.
abstract: 1. Autodegradation of yeast ribosomes is due to a 'latent' ribonuclease which is associated with the 40 S ribosomal subunit. 2. The ribonuclease was extracted in the presence of EDTA from ribosomes and purified 118-rold by protamine sulphate precipitation, (NH4)2SO4 fractionation and chromatography on DEAE-cellulose. 3. The optimum pH for this enzyme is 5 to 6.5 while the optimum temperature is 45 to 50 degrees C. Incubation for 10 min at 60 degrees C caused a reduction in enzyme activity of 70%. 4. The ribonuclease has an endonucleolytic activity against rRNA, tRNA, poly(A), poly(U) and poly(C) but does not degrade poly(G) or DNA. It hydrolyzes the homopolymers to nucleoside 3'-phosphates. 5. Zn2+, Mn2+, heparin, glutathione and p-chloromercuribenzoate inhibit the ribonuclease, while Na+, K+, EDTA and sermidine have only little or no effect. 6. It binds tightly to yeast ribosomes but only loosely to ribonuclease-free wheat germ ribosomes. 7. Polyribosomes possess less autodegradation activity than monoribosomes, isolated from the same homogenate.
mesh_terms: D001665:Binding Sites; D002412:Cations; D005978:Glutathione / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D012335:RNA, Ribosomal; D012260:Ribonucleases / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D012270:Ribosomes / Q000201:enzymology*; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D013379:Substrate Specificity
chemical_list: D002412:Cations; D012335:RNA, Ribosomal; D012260:Ribonucleases; D005978:Glutathione