i Hy 3s

ABSTRACT
Reprinted from Fec, Genetics Soc, Amer, Vis L546 )
(1948), ; aA Erp eral,
Lederberg, 3 M., University of Wisconsin,

ether
edison, View: The mutability of several Lace mutants
of Escherichia coli, -- Matants of 3B, coli unable to
Ferment Lactose nave been secured as descrided in
the next abstract, Some of these mutants (Lac-)

form colonics in which occur small, raised lactosc-
positive (Lact) areas. Independent occurrences of
loece mutarts vory in their revertibility, A segre-
gation for mutability was cbserved among tne recon
binant prototropns obtained when an unstable Lac
(Y-87)} was crossed with a stable Lace strain (#112).
A Lact vapilla was isolated from each cf 21 cclonies
of the most mmtable strein, Y-&7. Hach vas crossed
with wild type Lact, Of the 31,000 recombinants
examined all but one were Lact, Therefore, the
change from Iac- to Inc+ is vrobably a reverse
mutation, A sinilar study was initiated with the
occasional panillsae found in 028 colonies of the

most stable strain, Y-1l12, The strains isolated

were slow ferrnenters (Lac s), Lact, Lac s, anc

Lec- recombinants were obtained from crosses with

R sutton’ Tect, The Lac s cells from y.L12 thus
carry 2 "“suporessor" gene, A second distinct sup-
pressor leacing to full fermentation of lactose has
elso been found, Cne sicwv fermenter isolated fro
irradiated cultures of Y-&7 mutates rapidly to both
Lact and Lac-, Further studies on the fenetic
determination of metavility are in progress,