Crick here responded to Champe's report of results from his research with the rII mutants of the bacterial viruses T2
(phage) which had been used since the early 1950s in genetic mapping experiments. Crick himself discussed results of research
with acridine mutants of bacteriophage T2, a different family of mutants in whose study Crick's laboratory specialized
and which he used to provide evidence for the three-letter composition of the genetic code. The specific experiments to which
Crick referred were with acridine mutants called amber (the triplet UAA) and ochre (UAG) and with the triplet UGA, all three
of which signal the end of the polypeptide chain in protein synthesis.
Number of Image Pages:
2 (158,643 Bytes)
1967-03-06 (March 6, 1967)
Original Repository: Wellcome Library for the History and Understanding of Medicine. Francis Harry Compton Crick Papers
We were very pleased to get your letter, and learn the new information about the position of component 30. It certainly seems
that you do not pick this up unless the gene is working fairly strongly. We assume from what you say about the expected size
of the peptide that you have located the right-hand end of it, presumably by using amber mutants. Sydney is very keen that
you should try the effect of a UGA mutant to the right of component 30. We now have a weak suppressor for UGA and so we can
always obtain it wherever we have an ochre. It would be interesting to compare the effect of an ochre and UGA at the same
site to the right of component 30. If you will let us know roughly where component 30 is Sydney would be very pleased to
produce such a pair of mutants for you (we would probably also make the amber as well if we could). Of course, we would expect
that with an ochre or an amber there you should find a reasonable amount of component 30, but we are not at all clear what
to expect for UGA.
As far as I recall the evidence of last summer about the revertants of ochres turned out to be no good because when Sydney
looked into Anand's data the reversion rate was far too small to be significant.
Both Sydney and I would welcome William McClain in either the summer or fall of 1968 (it would not be possible to have him
earlier), so do encourage him to look into fellowships. I am asking Leslie Barnett to send you the mutants you ask for.
Sydney is very curious to know why you would like some of them!