December 4, 1964
Dear Dr. Watson:
Leon Heppel recently spent some time at Rockefeller with Zinder. Upon his return, Zinder gave him a slant of your ribonuclease--minus mutant (127?).  Both Leon and I would very much like to do some experiments with this organism. However, because we did not obtain the mutant directly from you, we would first like to be sure that our general plans in no way conflict with your own. If you have any objections to our use of the organism, would you please let us know.
In general, Leon is interested in using the mutant to extend his recent studies on enzymes that appear to be active on the surface of the cell. In this connection he is also using the ribonuclease--minus mutant MRE-600, which was kindly sent to him by Wade in England.
For my part, I am interested in looking at the activity of the soluble RNA-specific phosphodiesterase, in cells that lack the "ribosomal" ribonuclease. We already know that in MRE-600 neither diesterase nor polynucleotide phosphorylase activity is increased.
I am enclosing a few pertinent reprints.
With kindest regards,
Sincerely yours,
Maxine Singer