Nucleic Acids Research, 1980, Vol. 8, No. 21 5043-5055
© 1980
ENZYMOLOGY |
Purification and properties af DNA endonuclease associated with Friend leukemia virus
Department of Biochemistry, University of Bergen Årstadveien 19, N-5000 Bergen, Norway
Received July 14, 1980.
An endonuclease associated with the core of Friend leukemia virus (FLV) has been purified more than 103-fold by ion exchange chromatography and gel filtration. Its molecular weight was determined by gel filtration to be about 40,000. Divalent cations were required for the endonuclease to function and KCI concentration above 50 mM inhibited the enzyme activity. In the presence of Mg++ the purified enzyme nicked preferentially supercoiled circular DNA duplexes and in most of these molecules only one single-stranded nick was introduced per strand. The regions into which the nick could be introduced appeared to be randomly distributed on the circular molecule. When Mn++ was substituted for Mg++ the number of nicks introduced into DNA by the purified enzyme was greatly increased, and both relaxed circular and linear DNA duplexes were nicked as well as supercoiled circular DNA duplexes. Prior to its purification, however, in the presence of Mn++ the endonuclease activity in the virus extract was able to differentiate between circular and linear DNA duplexes, since both supercoiled and relaxed circular duplexes were nicked much more readily than linear duplexes. Single-stranded DNA functioned poorly as a substrate for the purified enzyme.
*Present address: Norwegian Food Research Institute P.O.Box 50, N-1432 Ås-NLH, Norway