Purification and properties of a light-inducible nuclease from Euglena gracilis

The nuclease described by Carell, E.F., Egan, J.M. and Pratt, E.A. [Arch. Biochem. Biophys. (1970) 138, 26-31] has been purified 1000-fold from Euglena gracilis strain Z. The enzyme catalyzes the hydrolysis of both polyribonucleotides and polydeoxyribonucleotides. The relative rates of hydrolysis of synthetic and natural polynucleotides was found to be: poly (U) 100, poly (dT) 33, denatured calf-thymus DNA 33, yeast tRNA 9, E. coli total RNA 6, poly (dA dT) 5, poly (A) less than 1, poly (C) less than .05, and poly (G) less than .05. The enzyme attacks polynucleotides in an endonucleolytic fashion, yielding products terminated with a 3'-phosphate. Poly (U) appears to be hydrolyzed completely to 3'-UMP; both RNA and DNA appear to have some phosphodiester bonds resistant to enzyme catalyzed hydrolysis. Because of its mode of action and its inducibility by light, we propose the name endonuclease L for this enzyme.