Letter from Francis Crick to Marshall W. Nirenberg
The amber and ochre codons mentioned in the letter (the triplets UAG and UAA, respectively) were called nonsense codons because
it became clear from experiments with certain phage mutants that they do not specify any amino acid during protein synthesis.
UGA was discovered to be the third nonsense codon, after Nirenberg had ruled out that it coded for either tryptophan or cysteine.
All three nonsense codons, Crick and others soon determined, instead signaled the termination of the polypeptide chain.
Robert Holley's experiments with soluble RNA, or sRNA, soon to be renamed transfer RNA (tRNA), were designed to sequence
the seventy-seven nucleotides of the tRNA that transferred the amino acid alanine during protein synthesis in yeast. These
experiments, carried out over seven years and not yet completed at the time of Crick's letter, showed how the shape of
tRNA made the molecule capable of capturing alanine and carrying it to the positions in the polypeptide chain where it was
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1965-06-08 (June 8, 1965)
Nirenberg, Marshall W.
Original Repository: Wellcome Library for the History and Understanding of Medicine. Francis Harry Compton Crick Papers
It was most kind of you to send the trinucleotides, which will be very useful. I was very glad to see that you had tested
UGA for Trypt and Cys. I am still very puzzled about Holley's s-RNA, as you will have seen by my wobble paper, and look
forward to hearing how it behaves in binding studies.
About the Gordon Conference. I have only two things to say. One is to report (in Sydney's absence) the evidence that
amber and ochre are UAG and UAA respectively. However this really comes under suppression, which I thought Lipmann was dealing
with. The other is "wobble" which is only worth about 15 minutes at the end of the session. The major omission from
your list is Yanofsky, who has some very important data (or is "Bekjanski" a slip for Yanofsky?). I imagine that
Holley will be talking in a different session.
I agree that there is no need for the summary to come from the Gordon Conference as such, but I think a joint letter, from
those people who happen to be there, would be very useful. Nothing need be put in that any author doesn't want quoted,
so the character of the Gordon Conference need not be affected. I'm not keen to write it all by myself, since all I have
done is to collate other peoples' work. Why don't we discuss it at New Hampton?
I have just written a letter to Abernathy suggesting that Grunberg-Manago, Khorana, Orgel, Zachau and Wittmann be added to
Information Exchange Group No. 7.