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The Lister Institute of Preventive Medicine

5 ; Chairman of the Governing Body : CHELSEA BRIDGE RO AD,
tR HENRY H. DALE, O.M., G.B.E., M.D., F.R.C.F., F.R.S.
Hon. Treasurer : LONDON, S.W.1.

Sir HuGH BEAVER, K.B.E.

Director : Telegrams : "Bacteriology, Knights. London”
PROFESSOR A. A. MILES, C.B.E., M.D., F.R.C.P. Telephone : SLOane 2181

4st August : 1964

Professor J. Lederberg
Department of Genetics
Stanford University
Palo Alto

California : U.S.A

Dear Professor Lederberg

Working on T,? mutants of E.coli K-12, I observed a pheno-
menon similar to the one you described in 1949 with V,°,type
resistant to Ty and sensitive to T5. My studies, begun with
Fredericq, have revealed that the mutation affecting the
strains used is probably a deletion extending, or not, to the
tryptophan locus. I suspect that the "Het" factor corres-
ponds to an abnormal chromosomal organisation, the effect of
which during pairing, is to delay segregation. Bem V g

7 ™M 1G

Dr. Stocker has suggested that I ask you for the strain ¥~
which gave you H-1, so that I could make more suitable
comparisons between your results and mine.

I should be very grateful if you could send me this strain,
and others which you think would help me in further studies,
also for any advice or suggestions you could give me on this
subject.

Yours sincerely

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