January 28, 1960
Dear Professor Kornberg:
In the course of the isolation of high molecular weight DNA from E. coli K-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 depolymerization is due to enzymes not requiring 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 degrading the DNA. I would be very grateful 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.
Sincerely,
Julius Marmur