The Synthesis and Breakdown of Nucleic Acids in Mammalian Cells Transformed by Oncogenic Viruses I. PURIFICATION AND PROPERTIES OF AN ENDONUCLEASE FROM BABY HAMSTER KIDNEY CELLS TRANSFORMED BY POLYOMA VIRUS

Abstract Continuous lines of baby hamster kidney cells transformed by polyoma virus (BHK21 C13/PyH3) have a number of nuclease activities. In order to understand how nucleic acids are synthesized and hydrolyzed by such transformed cells, a nuclease has been purified 1000-fold. The enzyme is optimally active at an alkaline pH (8.7 to 9.5) and hydrolyzes RNA and heat-denatured DNA. Native DNA is highly resistant to the enzyme. The RNase and DNase activities appear to reside in the same protein. The relative rates of hydrolysis of a number of synthetic polynucleotides, RNA, and DNA are as follows: polyuridylate (100), polydeoxythymidylate (71), polycytidylate (46), polyinosinate (33), polyadenylate (18), ribosomal-RNA (16), heat-denatured Escherichia coli DNA (7), transfer RNA (4), polydeoxyadenylate (2), polydeoxycytidylate (l2), and polyguanylate (0). The enzyme prefers, as substrates, polynucleotides which lack an ordered structure. The hydrolysis of polyadenylate or polydeoxythymidylate yields oligonucleotides with terminal 5'-phosphates. A concentration of 0.04 m NaCl or KCl inhibits the enzyme. The enzyme should be useful in preparing 5'-phosphoryl-terminated oligonucleotides from DNA. A similar enzyme appears to be present in a continuous line of baby hamster kidney cells (BHK21 C13).