THE UNIVERSITY OF WISCONSIN
COLLEGE OF AGRICULTURE

Madison 6

DEPARTMENT OF GENETICS

October 25, 1950.

Dr. 4. M. Doudoroff,
Dept. Bactericlogy,
University of California,
Berkelay 4s Balif.

Dear Hiico~

You could more expeditiously have gotten suitable cultures from K-12
from van Niel, who did a comparable claas experiment last sumasr, but I
am glad to send harsvitht

58-161 Bee (biotin; methionine) and

“L777 T-L-By-; Lace Mal- Xyl- Mtl- (lactose; maltose; d-xylose; mannitol};
v3" and 3",

As unselected markers I would use Lac +/- on EUB, and gt/s, The latter can
be carried out most conveniently by brushing a loopful of streptomycin solution,
about 20,000 units/ml, across andEwB plate. after this has dpied,.you-can cross~
atreak the purified prototrephs. The zone of inhibition of S can be as wide as
2 cm, so allow plenty of room. You can iliustrate lLinkuge very well and very
easily by also scoring for Mal. As you found yourself, Mal and 5 are very
Clossly linked.

Adequate directions are given in my 1947 Genetics paper. Inocula can be
taken directly from overnight, unshaken, cultures grown at 37. I find it/ now
more convenient to concentrate the washed culture from 10 to about 3 ml, and
to spread .05 mi of the mixture on the surface of minimsl agar, The plates
can be incubated at 37, and EMB plates, of course, mst be,

The resulte of such a cross should be about 70% Lace; 30% +3; 90% Mal~; 10% +3;
(with very little correlation, mesative cr positive), There che only a few percent
crossovers between Mal and S. ikl you let me know how it turns out?

fy the way, I find that I've completely run out of reprints of the coli~amylomal-
tase paper. If you hanpen to be able to spare them, I would appreciate any number
up to a maximm of 40 or 50.

Sincerely,

Joshua Lederbsrg_