title: A 5'----3' exoribonuclease of Saccharomyces cerevisiae: size and novel substrate specificity.
abstract: The purification scheme for a 5'----3' exoribonuclease of Saccharomyces cerevisiae has been modified to facilitate purification of larger amounts of enzyme and further extended to yield highly purified enzyme by use of poly(A)-agarose chromatography. As determined by either sodium dodecyl sulfate-polyacrylamide gel electrophoresis or physical characterization, the enzyme has a molecular weight of about 160,000. Further studies of its substrate specificity show that poly(C) and poly(U) preparations require 5' phosphorylation for activity and that poly(A) with a 5'-triphosphate end group is hydrolyzed at only 12% of the rate of poly(A) with a 5'-monophosphate end group. DNA is not hydrolyzed, but synthetic polydeoxyribonucleotides are strong competitive inhibitors of the hydrolysis of noncomplementary ribopolymers. Poly(A).poly(U) and poly(A).poly(dT) are hydrolyzed at 60 and 50%, respectively, of the rate of poly(A) at 37 degrees C. The RNase H activity of the enzyme can also be demonstrated using an RNA X M13 DNA hybrid as a substrate. When poly(dT).poly(dA) with a 5'-terminal poly(A) segment on the poly(dA) is used as a substrate, the enzyme hydrolyzes the poly(A) "tail," removing the last ribonucleotide, but does not hydrolyze the poly(dA).
mesh_terms: D005095:Exoribonucleases / Q000302:isolation & purification / Q000378:metabolism*; D008970:Molecular Weight; D012330:RNA, Double-Stranded / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D013379:Substrate Specificity
chemical_list: D012330:RNA, Double-Stranded; D005095:Exoribonucleases; C022535:exoribonuclease II