November 11, 1957
Dear Maxine:
Thank you very much indeed for the slides and the copy of your talk to the ACS meetings in September.  Although I had read the abstract I certainly enjoyed reading the full talk with the beautiful slides. This will help me very much in my lectures on polynucleotide phosphorylase. The priming story would be very incomplete without the beautiful work that you people did.
Regarding the preparation of polynucleotide phosphorylase, we are still bogged down trying to get once more good active extracts and ammonium sulfate fractions therefrom.  We do not know exactly where the trouble lies but in the past few months we haven't had much luck and have gotten preparations of low specific activity unsuitable for the further steps.  I hope we shall be able to clear this up in the near future and, once we are ready to go through with a preparation, I will let you know so that you can come over and spend a couple of weeks with us.  It will be a pleasure to have you around.
With best regards,
Sincerely yours,
Severo Ochoa