GENE RECOMBINATION AND LINKED SEGREGATIONS 

 IN ESCHERICHIA COLI 1 



JOSHUA LEDERBERG 2 



Department of Botany and Microbiology, Osborn Botanical Laboratory, 

 Yale University, New Haven, Conn. 



Received August i, 1947 



THE occurrence of factor recombination in the bacterium, Escherichia coli, 

 has been described in previous reports (Lederberg and Tatum, 1946 b, c, 

 Tatum and Lederberg, 1947). In an attempt to elucidate further the genetic 

 structure of this organism, these studies have been extended to crosses involv- 

 ing several characters, and to the quantitative enumeration of various recom- 

 bination classes. The results described in this paper provide evidence support- 

 ing the sexual basis of factor recombination and of the existence of an organ- 

 ized array of genes comparable to that of higher forms. 



MATERIALS AND METHODS 



The parent "wild-type" strain, K-12, of E. coli used in these experiments 

 and the production and behavior of biochemical mutants have been described 

 (GRAY^nd Tatum, 1944, Lederberg and Tatum, 1946a, Roepke, Libby, and 

 Small, 1944, Tatum, 1945). Specific requirements, notation, and other data 

 pertinent to the biochemical mutants are summarized in tables 1 and 2. In gen- 

 eral, a biochemical deficiency resulting from mutation is designated by the 

 initial of the substance required (e.g. B~ for biotinless), while the wild type 

 alternative is written with a " + " sign (e.g. B + to emphasize the alternative to 

 B~). The term "prototroph" (Ryan and Lederberg, 1946) has been devised 

 for strains exhibiting the nutritional behavior of the wild type, which for E. 

 coli implies independence of any specific growth factors. Prototroph is, how- 

 ever, not synonymous with "wild type" since it refers (a) only to the pheno- 

 typic appearance of a culture and (b) only to nutritional and not to other pos- 

 sible mutant characteristics. 



K-i 2 as a coliform is capable of fermenting, or producing acid, from a variety 

 of sugars, including glucose, galactose, maltose, lactose and mannitol; how- 

 ever, it ferments glycerol only weakly, and sucrose even less so. Because of the 

 ease of scoring and their biochemical specificity, mutants unable to ferment 

 various sugars have been looked for. Particular attention was paid to the isola- 

 tion of "lactose-negative" or "Zac - " mutants, because of the taxonomic sig- 

 nificance which has been attached to this character. 



1 Abstracted from a dissertation offered in partial fulfillment of requirements for the degree 

 of Doctor of Philosophy at Yale University. 



2 Fellow of the Jane Coffin Childs Memorial Fund for Medical Research. This work 

 has been supported by the Jane Coffin Childs Memorial Fund for Medical Research. The 

 author's present address is: Department of Genetics, University of Wisconsin, Madison, Wis 



[Reprinted by permission from Genetics 32:505-525, September, 1947] 



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