July 13, 1958

Dr. Severo Qchoa
Villar
Lucarca, Asturias,
Spain

Dear Dr. Ochoat

Thank you very much for sending your comments on the manu-

script.
manuscript and I'll send it to Canada this week.

1 have incorporated your suggestions into a corrected

The reproduction of the chromatogram photographs was pro-

bably not too good in the copy I sent you but the areas that
you referred to are, in fact, visible on photographs of Figure 9,
I will have to be careful, however, in chocking the proof to be
sure all the spots can be seen.

Dr. Heppel is off in British Columbia and Russ and I are

busy finishing up some experiments we did with Marianne.  I hope
to write up a rough draft of a paper including this data and
send it off to you so that you can, if you like, use some of the
information in your talks later this summer. The experiments
concerned exchange with GDP, the stepwise mechanism of phosphor-
olysis, and the effect of 3*-ended oligonucleotides on the rate
of phosphorolysis of the 5*-ended ones. Surprisingly, although
they inhibit the phosphorolysis of the 5'-ended, the inhibition
is not very striking,  It is best when the 3'sended is a longer
chain, ish.; ApApApUp on pApApA.  We have also found that poly
A inhibits exchange with UDP and poly U inhibits exchange with
ADP - a situation similar to the results with polymerization.

  Regards to you from Russ and from Dan.
Whoa continue having such a pleasant trip.

We hope you and Mrs,

Sincerely,

Maxine Singer