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Embryology and the Organization of DNA in Higher Organisms, 1966-1976
Letter from Francis Crick to Severo Ochoa (February 21, 1967)
We have been tickled by your recent paper in Nature on UGA. We tried a few times whether this triplet would code for anything
with oligonucleotides of the type AAAUGAAAA . . . AAA and got negative results with both tryptophan and cysteine. As you
may remember, the cell-free system misses the 5'-end triplet in such polymers but translates the others. It would be
interesting if UGA indeed functions as a spacer triplet between genes. In some of my lectures I have been writing UAAAUG
for the end and beginning of cistrons, respectively. Do you think it is going to be UAAUGAAUG?
We have now good evidence that, upon translation of MS2 RNA by the E. coli system, both the coat protein and the synthetase
are initiated with formylmethionine. We do not get intact maturation factor protein in vitro, probably because of nucleases
in the system. We also have final proof for UAA as a chain termination codon. On translation of polymers of the type AUGUUUUAAAAA
. . . AAA, the cell-free system forms formylmet-phe in good yields, as the free dipeptide released in the supernatant.
I am going to be in western Europe this spring and I am planning to visit England the last week in April. I would of course
like to take this opportunity to spend a day in Cambridge. Would April 27 or 28 be convenient?