Geneva, May 13, 1957
UNIVERSITE BE G
Quai da {Ecoie-de-Médecine

GENEVE

Prof, J. Lederberg
Dept of Genetics

University of Yisconsin

 

Madison 6

Wisconsin USA

Dear Professor Lederberg,

Under separate cover and by ordirary mail, we sent you a
“S about some of the defective strains we studied. We would be very glad
to have your comments and criticisms. We intend to rewrite a better dis-
cussion, which we will soon send you. Several sentences in the text are

badly written and can be misunderstood; we beg your pardon.

My wife has recently reinvented the Tetrazolium-indicator-
agar for Galt plates! Blie Wollman and Jean Yeigle draw our attention on
the fact that you described the use of thdéds substance long ago. There is
one very surprising difference between your results and ours: in our nu-
merous experiments, always the Gal-fermenting colonies mark in dark red,
while the non fermenting become faintly coloured only much later. Comna-
rison with sR gives coherent results, but results with Tetrazolium plates
are much clearer and more rapid. fhe Py of the medium (between 6.3 and
7.8) vroved to be of no influence on the discrivination. Fe would be glad
to have your comments on this problem and we would like to know the rea~

sons why you do not encourage the use of this method.

The work on Gal-defectives is progressing. The latest re-
sults indicate that all phages carrying the marker Galt are defective.
Upon lysogenization they produce obligatorily a defective-lysogenic Galt.
Upon lytic development they do not produce mature phage, unless a second,
normal vnage is also developing in the same bacterium (giving the oppor-
tunity for phenotypical miming). Therefore the Gal marker seems to com
pete with nart of the ~hage-genome, vart which is essential for coat forse
mation. A further hyvothesis coming out of the work of ". Arber and my
wife is that probably Gal* lysogenic prodtcing Hfr transducing \ (hetero-
genotes) are doubly lysogenic for a defective Galt carrying phage and a

normal .

Veg sincerely yours