Carl: Please take care of this and let me know AK
May 11, 1962
Dear Arthur:
We have obtained ultracentrifugally homogeneous preparations of RNA polymerase from Azotobacter after about 500-fold purification and would like to check the copying activity of this enzyme with poly dAT and poly dCdG as primers if you could spare some of these precious materials.  We have previously done some experiments with the poly dAT that you kindly sent me last summer.  Unfortunately, we spent most of this sample in making poly AU to try for amino acid coding.  It did not work probably because of double-strandedness.  HN02-treatment of the poly AU, which should have yielded poly IU, also resulted in an inactive product.
We enjoyed seeing you at the White House.  It certainly was a memorable, most enjoyable occasion.
With our fondest regards to you, Sylvia, and the children, as always,
Yours,
Severo Ochoa