The deoxyribo-nucleases of Escherichia coli. III. Studies on the nature of the inhibition of endonuclease by ribonucleic acid.

It was first observed by Kozloff (1) that the deoxyribonuclease activity of cell-free extracts of Escherichiu coli could be increased by treatment with pancreatic ribonuclease. This stimulation was found to result from the destruction by the ribonuclease of an inhibitory ribonucleic acid. The phenomenon of cellular deoxyribonuclease inhibition is a widespread one, having been observed in yeast (2), mammalian tissues (3), and streptococci (4). The yeast and mammalian deoxyribonuclease inhibitors were identified as proteins; the streptococcal inhibitor was shown to have the properties of a ribonucleic acid. Recent investigations of the nucleases of Escherichiu coli (5, 6) have shown that the deoxyribonuclease activity in cell-free extracts of this organism is attributable to at least three different enzymes. Two of these have now been purified. It was, therefore, of interest to establish which of these enzymes is subject to inhibition by ribonucleic acid and what is the nature of the ribonucleic acid-enzyme interaction. The studies reported here show that the deoxyribonucleic acid-specific endonuclease described in the previous paper (6) is the only one of the known nucleases of E. coli which can be inhibited by ribonucleic acid. They further demonstrate that ribonucleic acids from a variety of sources, including E. coli, guinea pig liver, and tobacco mosaic virus, can serve as potent inhibitors of the purified endonuclease.