April 15, 1969
Dear Marshall,
I know that you are no longer doing work on the Genetic Code, but I would like to get a favor from you if it is possible.  We are in the midst of trying to identify a new suppressor of UAG which we have isolated.  We are almost sure that it inserts glutamine, but in contrast to the usual su2 suppressor, this mutation is lethal for the organism.  We can carry the mutation in diploids and therefore have been able to study the mechanism of its suppression.  In trying to extend this work to in vitro suppression, we have used the f2 sus3 mutant and looking for tRNA-dependent suppression in vitro.  We would also like, if we can, to show the suppression by triplet binding, but we are not such good chemists that we can quickly make appropriate triplets.  I wonder, therefore, if I can prevail upon you to get some.  What we would like to have is some UAG and CAG.  We would like to be able to fractionate the suppressor species and monitor that fractionation by the coding response.  If you could let us have some of each of the two triplets, it would very much help our effort.
Hope to see you soon,
Sincerely,
Paul Berg