December 10, 1946.

Dear Dr. Iuria:

Further attempts to demonstrate different virus resistance
patterns in our E, coli continue to show 1,3,5 as the only
type of resistant colony obtained after plating with ?-1l.
K/7 shows no cross-resistance. An attempt to analyse the
1,3,5 resistance complex genetically, by crossing a K/ 1,3,5/7
with a sensitive strain gave recombination between the ta and
71,3,5 resistance factors, but the 1,3,5 complex remained intact
in some 100 isolates of recombinant cells.

Have you any information on resistanee patterns in K-12?
There are some rumours around New York that you have discovered
an ‘allelic! series: I just thought you'd be interested to her
thisy- I hope to meet you in Bos$on for Christmas.

It may be of interest that in a cross:

B-U-T+1+B)+Lac+?j by the corresponding ++----S, that all
& recombination types of the factors B,; Lac; and T) have been
isolated, with widely different frequencies, continuing to sugcest
linkages with a map roughly: By -BoMo os LaceseeTy ose ePePy
This is still very much a speculation, but linkages of factors
on a single chromosome continue to provide the best explanation
for the frequencies of various types.

With best regards, especially to Sonneborn,

Sincerely yours,

Joshua Lederbe rg.