Acknowledgment.-The author is grateful to Mr. of tile J. p. vizsolyi for technical assistance ill experilnents reported here. nucleotides terminated in 5'-phosphornonoester groups are resistant to this enzyme' XTANCOUVER 8, BC, CANADA ... (23) It has previously been determined by LA Hcppel and RJ Hilmoe (“Methods in Enzymology,” Vol. 11, 1965, p. 665) that di- ... [CONTRIBUTION FROM THE DIVISIOX OF CHEMISTRY, BRITISH COLUMBI.4 RESEARCH