| Abstract: | We have extensively purified from Krebs II ascites cells, although not until homogeneity, a ribonuclease which preferentially cleaves natural or synthetic double-stranded RNA substrates (RNase D); this specificity is also supported by its sensitivity to inhibition by 10(-5) M ethidium bromide. It does not degrade RNA-DNA hybrids and is, therefore, clearly distinct from previously characterized RNases H (Cathala, G., Rech, J., Huet, J., and Jeanteur, Ph. (1979) J. Biol. Chem. 254, 7354-7361). It shows no requirement for a divalent cation and is inhibited by all kinds of nucleic acids regardless of their secondary structure. It acts exclusively as an endonuclease, as shown by the analysis of degradation products, and yields 5'-phosphate termini. This enzyme is able to introduce discrete nicks into purified HeLa 45 S preribosomal RNA as well as into HeLa heterogenous nuclear RNA packaged within naturally occurring nuclear ribonucleoprotein particles. It is, therefore, an interesting candidate for an RNA-processing enzyme. |
