Q20

. LEDERBERG, ESTHER M,, University of Wisconsin, Madison,
Wis.--The inheritance of lysogenicity in interstrain crosses
of Escherichia coli.--Of 50 diverse fertile strains, four
proved to be sensitive to and lysogenized by the bacterioe
phage lambda carried by strain K-12. Crosses within these
strains indicate an Lp locus determining lysogenicity and
linked to Gal as in K-12, Each new strain lysogenized by
lambda shows a more limited output of plaques when tested
on Ke12 than on the other sensitive indicators. Similarly,
Kel? is more resistant than the other sensitives to free
‘lambda originating from the other strains. By testing for
sensitivity to both sources of lambda, and for lysogenicity
on each indicator, four phenotypes are delineated: two
lysogenic and two sensitive, These relationships are
analogous to the host-induced modifications of lambda de»
scribed by Bertani and Weigle (J, Bact. 45, 113), When-
ever lysogenic x sensitive crosses involve K-12 as one.
parent, all four possible recombinant classes are fountin
the progeny, thus establishing a second locus, Mp. which
modifies the expression of Lp. Kel2 occurs as pf Lp*
(1ysogenic) or MpTLp® (sensitive); the other four strains
as p* (modified lysogenic) or Mp®Lp® (modified sensi-
tive), Linkage of Mp to the Lp-Gal loci was not demon-
strated, Crosses reciprocal with respect to F (compati-
bility factor) differed in yield but not in the type of
recombinants, ‘The absence of sensitives from crosses of
lysogenics segregating for Mp makes it likely that lambda
prophage remains fixed to Lp, rather than Mp, in all lines,

Reprinted from Genetics, 392978, 195h,