Complementation, Recombination, and Suppression in Galactose Negative Mutants of E. Coli.

The metabolism of galactose in Escherichia coli proceeds via conversion of galactose to glucose-i-phosphate by reactions catalyzed by the enzymes galactokinase, galactose-l-phosphate uridyl transferase, and UDPgalactose-4-epimerase.1 In addition to these reactions specific to galactose metabolism, the ability of the bacteria to utilize galactose depends on the production of catalytic amounts of UDPG and on the interconversion of glucose-l-phosphate and glucose-6-phosphate by reactions catalyzed by UDPG pyrophosphorylase and phosphoglucomutase, respectively.I Mutants unable to utilize galactose for growth have been isolated by E. M. Lederberg, J. Lederberg, and M. L. Morse.2 A number of these mutations have been classified into functional groups (cistrons) by complementation pattern in Xdg partial diploids in which the temperate phage Xdg provides the bacterium with "extra" galactose genes.3 Some of the mutants have also been characterized with regard to enzymatic defects in kinase, transferase, epimerase,4 6 and, more recently, pyrophosphorylase activities.6' I Adler and Kaiser have genetically mapped many of these mutants, utilizing recombination between transducing phage PI and the bacterial chromosome,8 and Morse in another mapping study has used recombination between Xdg and the bacterial chromosome in Xdg partial diploids.9 Buttin has genetically mapped some independently isolated galactose negative mutants using Hfr by Fcrosses.'0 The present report describes complementation, recombination, and suppression observed in FGal partial diploids heterozygous for two different galactose negative (Gal-) mutations. This study has utilized many of the "classical" Lederberg Galmutants plus some 60 new mutants. In addition to the genetic results, enzyme measurements for the five enzymes of galactose metabolism described above are given for some of the newly isolated mutants representative of different complementation groups. Materials and Methods.-Bacterial strains and crosses: Haploid galactose negative (Gal-) mutants were either representatives of the Lederberg collection (via J. Adler),3 8 or mutants isolated for the present study by penicillin selection and plating on EMB galactose. The new mutants were derived from a relative of the Lederberg W1 Fdesignated F3W1, and are designated by the prefix G (e.g., Gl, G45A, G64D). The Lederberg Galmutations are designated by their traditional nomenclature as Gall, Gal2, etc.3 The "W designation" of the Lederberg strains used in this work (e.g., W3102) is given in the paper of Adler and Kaiser,8 except for Gallo (W4666). Heterozygous partial diploid strains were prepared from these Gal mutants by crosses between FGal donor bacteria (F' strains) and Frecipients." 12 The designation FGal means that the structural genes for kinase (k), transferase (t), and epimerase (e), and an operator control locus (o)the classical Gal operon-are transferred with the F episome. The resultant partial diploid is represented as FGal +/Galbif the donor carried FGal + (Fk +t +e +o +) to a Galb F -, or FGala-/ Galbif the donor carried FGalato a Galb-F(Gal.and Galbrefer to any mutations in the k t e o operon). The FGal + donor used was strain F'8 of Hirota. 12 Homozygous FGal.-/Gal.donor strains were prepared from heterozygous FGal+/Gal.by isolation of segregant Galcolonies. These segregant colonies, which could be either diploid FGala-/Gal.donor strains or