UNIVERSITY OF CAMBRIDGE

PROFESSOR R. A. FISHER, Sc.D., F.R.S. DEPARTMENT OF GENETICS WHITTINGEHAME LODGE
MISS M.F.L SPEYER, B.Sc. ’
Research end Secretary 44 STOREY’S WAY
CAMBRIDGE
Tel, 35822

Oct 31st, 1949

"Dear Lederbere,

Thank you very much for your last two letters and your new strains,

“hich T have had just the time of testing in the two weeks since I an back to

Cambridge. |

Pog ge In trying to repeat your experiments ,crossing W 1059 x W814 ,

since the mixture was incu
I have fodlowed for the first four days/all possible combinations of Sugars,

Xylac,Galac etc. hesides Malac. I was alittle surprised to see practigally no

trace of recombinants on these media, but I did not give great importance to ,

this discrepancy from your: results, because,as you tell me in your second letter,

it ‘must be that
mest of this effect is due to selection of some recombinants, and obviously/my

cultures show different selection conditions for yours. The mixture had been

oO s oe .
incubated in7Et Pao" nutrient broth{adjusted at pH 7.3); are you using perhops a
glucose broth ? If so, pH may have an importance in the question. I repaated the

experiment,but with no suecess,even making daily transfers rather than allowing

the culture to age. I am interested in this experiment because it may give an idea
of the rate of recombination when it is not needed, therefore when it happens spon-
taneously. I am trying to follow now the effect of pH and salts on recombine tion
in minimal, and I shall let you know about it; though you probebly have an |

experience in the mma&ter.

T could definitely find no trace of greater ultraviolet resistande”
of the Hfr strain ,repeating experiments now. The curve is of multi-hit type. I

have not yet any information about X-ray curves.

Did you get 123 through the National Collection of Type Cultures?

tf not,and if you are still interested in it,please let me know. It is giving me

some headaches,because I am held up with it that by the fact that IT can't find

its growth requirements; either they sre very complex,or involve growth

factors still unknown,or perhass only unknown to me,or they it eed common
facbérs in unusual concentration. It is also very aifficult to obtain

back mutetion to prototrophisn.
The cytological analysis is still at its very beginnings. In the same condition
‘is work with antigens 3; When T left I had-only a serum egainst K 12,which agglutinated
WM ot a 'sligttly smaller concentration (probably an antienpsuler serum).

eT should: Be very interested to have. some of your Het stocks,for the following

. used: a) testing allelisn of some Lac- and ve mutants | obtained in 58-161 and 123 ;

>

‘ard in this case, some hintS/ to, the most expedite way for ferforming this tess ; b),

   
 

4" T can find time to cope with it, I should like to use Het to sesk check the very
ola and peebably ‘possibly wron# theory that ultraviolet and X-ray Villing «is due to
-' the ‘induction of lethal mutations. ‘The - Het, stock should help to cope with the reces-—
[ive | ‘ones “at Least, ‘and there’ ‘were some hints: at it in your paper on the Prod.N.4.S.
Fhease. dont. ‘nesttate to ‘refuse this sit ik is of any inconvenienee to ous « ve

. ae

“Tt am yours sincerely

tb Samat

 

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