February 9, 1960

Dr . Julius. Marmur
Department of Chemistry
Harvard Univer sity
12 Ward Street
Cambridge 38, Massachusetts

Dear Dr. Marmur:

Dr. Kornberg has asked me to reply to your letter of January 28.

We have identified three distinct nucleases acting on DNA in E.

-- coli Ei
absolute magnesium requirement.
which has either been heated or partially degraded with the first nuclease
or pancreatic DNase.
the absence of added magnesium.
active in the presence of . 01 M Versene.
the third nuclease, but it too appears to be inactive in the presence  of
Qersene.

One of these, which is active on intact DNA, seems to havean
                A second enzyme acts only on DNA

It shows about one-fourth of maximal activity  in

           We have done very little with

It is, however, almost completely in-

   To answer your question then, the nucleases that we have identified
in E.  coli B. would not be expected to show much activity in the presence
of Versene.  The situation with regard to K-12 however, may be different.

-

We have been able to isolate D&A froni E.  coli 8. which seems to be

-

reasonably good, with E (p) values of 6. 4 - 6.3 and reduced viscosities
ranging from 45 - 60 deciliters per gram.
used the Duponal procedure of Zamenhof, modified as described in  our
article in the Proc. Natl. Acad. Sci. - 44, 1191 (1958).

In these isolations we have

Sincerely yours,

I. R. Lehman

1RL:ms