Jean Weigle:
California Institutebef Technology
Pasadena 4, California

Dear Dr, Weigle:

We are sorry to havetdelayed sc long in reply to your letter of
las Chrishmas week. In fact, we had already been working on the €1ikely)
possibility that these lines do carry cther phages, end veinly hoped we
could clarify the situation in time to send you the informetion along
with the cultures. This was too optimistic; but don't be surprised if
new phages crop up.

Our interest in this point is only distantly related to yours: we
have been crossing the lines to study "Mp" (see abstract enclosed) which
may still prove to be the locus of another prophage, comparable to Lp/lambda.
That host-modification and phenotypic mixing are related is already suggested
in the typing phage system of Salmonella typhi, and we would not be astonished
if, as you suggest, your "mutants" take their place in the same pattern.

Enclosed are %-~1827 and ¥-2085. The former 1s from a aerles of isolates
from human sources collected by Dr. R. 5. Benham at tha University of Chicago
Hospitals; the latter from a similar collection from the Wisconsin State
Public Health Laboratory. As ofiginally isolated, the strains were not
sensitive to lambda: the present isolates are cultural variants which are.

As these subcultures are from an old atock, you may have to look them over
Garefully. *"e suspect that lambda and the T-phages are "rough specific" for

£. coli, since very few if any of the freshly isolatad, antigenically com-
plete stocks that we have studied are sensitive to theses phages, while rough
variants mora often are. If one purposely Looked, £98 F2 Yariants, one would
probably find a higher incidence of lambda-senaltives ng ‘lew collections

of strains.

We would be obliged to you for mutants of lambda and information on scoring
them, as you offered. For our studies, on the lysogenic state rather than
the lytic cycle, we would need lambda mutants that do not necessarily kill
the hosts that they infect; mutants that can superinfect Lp would be ef
some use, even if they were virulent for Lp®. The lambda-2 that we sent
you some time ago is inapplicable. We had contemplated, but never really went
to work on, a search for such markers, and your material and advice would
be appreciated.

We are very sorry never to have had the occasion of meeting you, and hope
you will some time consider stopping over at Madison en route to or from
Calteck. Yours sincerely,

Esther M. Lederberg