Open AccessA Ribonuclease H from Ustilago maydis
Author(s) -
BANKS Geoffrey R.
Publication year - 1974
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1974.tb03718.x
Subject(s) - ribonucleotide , dna , rna , ustilago , polynucleotide , biochemistry , ribonuclease , enzyme , biology , endonuclease , chemistry , nucleotide , gene
A ribonuclease, which can degrade about 90% of the RNA strand of an RNA · DNA hybrid, has been extensively purified from Ustilago maydis. It is highly specific for a calf thymus RNA · DNA hybrid, little or no degradation of the RNA strands occurring after heat denaturation of the hybrid, or of single and double‐stranded DNA. With the exception of poly(rU) · poly(dA), all the ribonucleotide strands in hybrid homopolymers were susceptible to degradation, the double‐stranded homo‐polyribonucleotides being resistant. Both poly(rU) and poly(rI), however, were degraded. The enzyme possesses a molecular weight of 1–130000 and requires magnesium ions, ammonium sulphate and a sulphydryl reagent for maximum activity. It is an endoribonuclease, releasing oligoribonucleotides terminated by 5′‐phosphate and 3′‐hydroxyl groups, but is unable to remove a ribonucleotide covalently joined to the 3′‐terminus of DNA. Two mutant strains of U. maydis , which are temperature‐sensitive for DNA synthesis, possess elevated levels of the enzyme. This organism contains at least two other enzymes which can degrade the hybrid substrates.