HARVARD UNIVERSITY

DEPARTMENT OF CHEMISTRY

    12 Oxford Ssreet
Cambridge 38, Massachusctzs, USA.
  January 28, 1960.

Professor Arthur Kornberg
Department of B i oc hem i s t ry
Stanford University Medical School
Stanford, California

Dear Professor Kornberg:

In the course of the isolation of high molecular weight DNA  from

E. coli X-12 we have encountered degradation which we believe to be due to
DNAase or other nucleases. Since these preparations have been carried out
in the presence of citrate and versene,'*it is very likely that the de-
polymerization is due to enzymes not reouiring metal ion cofactors.

Perhaps you have had some experience with these latter enzymes  in

extracts of E. coli and would know how to inactivate them without degrad-
ing the DNA. I would be very greatful for any information that you could
give me concerning this problem.

This work is well under way and we would be very appreciative if we

could hear from you as soon as possible.

S i nc ere ly ,

JM/C s