PT lettre loot.

ABSTRACT

Reprinted from Rec, Genetics Soc, Amer, 17: 46 (1948)

Lederberg, Joshua, University of Wisconsin, Madison,
Wis.: Gene control of B-galactosidase in Escherichia
coli, -- A large series of B-galactosidase mutants of
E. coli was obtained by irradiating heavy cell suspen
sions on the indicator medium, EMB Lactose Agar, The
mutants were compared phenotypically and genetically
(see Genetics 32: 505). Most of the mutants involved
the locus Lac, and were phenotypically alike (lactow-,
methyl galactoside slow), Altogether, however, at
least seven and provably ten distinct loci were found,
mutation at any one of which leads to the loss or
alteration of galactosidase, Two of the mutant types
have additional effects: Lac-~ fails to split maltose
or to ferment gluconate; Lacz- to split ialtose or to
ferment glucose, galactozymase remaining intact, Sev-
-eral distinct mutations which partially "suppress"
Lacz- have been found, leading to such phenotypes as
Lac-Mal-Glu+, LactMal-Glu-, and even Lac-Mal+Glu-,
While the latter suggests the direct or phosphoryla-
tive utilization of maltose, other evidence suggests
that lactose is initially split by galactosidase,

An allele of Lacz+ has been found which is temperature-
sensitive, showing different thresholds for the fermen-
tation of sorbitol, of glucose or maltose, and the
splitting of lactose, and pointing to the pleiotropic
effect of the mutation, The complex gene-enzyme pat-
terns suggest that some mutations have indirect effects
on the production of one or more enzymes, It will be
difficult, therefore, to point to a given gene as the
source of specificity of a given enzyme, even though
its mutation leads to the loss of that enzyme,