Crick here commented on Champe's attempt to find the protein for which the rII mutant of the bacterial virus T2 coded.
Crick himself discussed results of research with acridine mutants of bacteriophage T4, 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
Crick named the various strains of acridine mutants, which he had initially produced in 1961, by assigning to each one a number,
preceded by his initials, such as FC58. He explained that he had done so not for self-aggrandizement but to aid him in organizing
and remembering the many different strains.
A cistron denotes the smallest unit of genetic material that must be intact to serve as a transmitter of genetic information,
i.e. which determines the sequence of amino acids in one polypeptide chain. Gene and cistron are sometimes used interchangeably.
Number of Image Pages:
2 (186,715 Bytes)
1966-10-24 (October 24, 1966)
Original Repository: Wellcome Library for the History and Understanding of Medicine. Francis Harry Compton Crick Papers
We were very pleased to get your letter. Component 30 looks very convincing indeed and we are all eagerly waiting to hear
that you have found the B protein tips.
We have looked up the mapping data on FC 58 and we agree with you that there is something fishy about it. Leslie crossed
FC 58 with a special derivative of 1589. This is X25 + 1589. X25 is an ochre in the A cistron close to the beginning of
1589. This knocks out the A cistron and thus should make the mapping easier. The cross with FC 58 showed a small number
of recombinants although this was not done quantitatively. What is embarrassing however is that FC 201 gives a clear positive
result on spot cross with X25 + 1589. In addition FC 201 lies under 1231. This and all the other data for the mutants in
that region suggest that FC 201 is to the left of FC 58, in which case FC 58 should give a strong positive result with X25
+ 1589. At the moment we are unable to explain this anomaly.
If things had turned out as we expected we should have been able to send you a copy of the completed paper. It has all been
completely typed and all the figures and references etc. finished. The only remaining thing that had to be done was to check
an entry in one of the tables. This was to make sure that X655 did not revert to ochre. When Leslie checked this we were
astonished and delighted to find that it did. This made us suspect that our previous attempts to revert some of the barriers
in this way might have been inadequate. She has just found that barriers b5 and b6 also revert to ochres. This makes it
extremely likely that our third class of nonsense triplet, which previously we had been unable to identify, is UGA. We are
now exploring this intensively and have decided to hold up the paper until it is all sorted out as we shall have to rewrite
one or two sections which deal with the nature of the barriers this way. However, I have asked Leslie to send you a copy
of the map and we will let you have the complete paper in its revised form in a few weeks time.
I have also asked her to send you the following mutants:-
X25 + 1589
FC (l + 222)
FC 222 is the plus mutant at the extreme right of our region. It gives a minute when combined with FC 1.
If there is any other information you want to know in relation to mutants that you would like us to send you please do not
hesitate to ask. As you can imagine Leslie is very occupied just at the moment so I doubt if she will look into the mapping
anomaly of FC 58. Do let us know anything that you find about it.