Crick here briefly touched on research with acridine mutants of bacteriophage T4, experiments that demonstrated that the
triplet UGA did not have a transfer RNA assigned to it, meaning that it coded not for an amino acid but for the end of the
polypeptide chain in protein synthesis.
NOTE: The right margin of the orginal letter cuts off a portion of the text.
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1966-11-02 (November 2, 1966)
Original Repository: Wellcome Library for the History and Understanding of Medicine. Francis Harry Compton Crick Papers
I enclose a copy of our paper. From its weight alone you can see why it has taken us so long to produce it. I think I need
only make two comments at this point. First, we have not said anything in it about the anomalous mapping of FC 58 we thought
we could put this in proof when things are a little clearer. Second, we have removed from our earlier draft some of our remarks
about the identity of the barriers as we plan to publish this in a separate paper. It now seems almost certain that X655
together with barriers b5 and b6 are UGA, and we hope to know very shortly whether b2 is the same. We are also going to try
to put an amber in place of barrier b6 and see if this will produce minutes when combined with two suitable plus mutants.
If it does not this will suggest that the production of minutes does not depend on chain termination. Our present case is
that there is no tRNA for UGA.
How are you getting on in your search for the rII protein?