Section 4 — Gene Action 



mined antigenically) produced by the parent 

 strain. These changed inducible levels of isome- 

 rase, epimerase and kinase CRM vary coordi- 

 nate^. It is proposed that coding in the B gene 

 besides determining the structure of L-ribuloki- 

 nase may set the rate of production of the mes- 

 senger for kinase, isomerase, and epimerase. 



4.7. Complementation of Arabinose Negative Mutants 

 of Escherichia coli. R. B. Helling (Pittsburgh, 

 U.S.A.). 



L-arabinose non-utilizing mutants of E. coli, 

 strain B/r, fall into four groups. A mutant in 

 group A, B, or D lacks one of the first three 

 enzymes involved in arabinose breakdown, while 

 gene C mutants lack all three enzymes. ^ 



In order to study the complementation pattern 

 of these mutants using sexual merozygotes, the 

 mutant sites were transduced from E. coli strain 

 B/r (which mates poorly) to E. coli strain K-12, 

 which had the arabinose genes of strain B/r. 

 Induction of arabinose enzymes was measured in 

 merozygotes obtained from a cross involving 

 two different arabinose negative mutants, under 

 conditions where neither parent could produce 

 the enzyme. Four complementing groups were 

 found which corresponded to the four known 

 genes. Each group complemented all other 

 groups; thus C gene mutants are not similar to 

 known operator or regulator mutants, and gene 

 C produces a cytoplasmic product necessary for 

 the induction of the arabinose enzymes, possibly 

 a permease. 



zyme map within two separate segments of gene 

 G. (») 



Enzyme production is coordinately repressed 

 in the presence of L-histidine ^ or 1,2,4-tria- 

 zole-3-alanine (TRA). Both compounds elicit 

 pyrophosphate exchange reactions, activities 

 which are not repressed by L-histidine. (5) TRA 

 allows synthesis of afunctional proteins in histi- 

 dine auxotrophs and is recovered from protein 

 hydrolyzates. ( 6 ) Mutations at (a) gene(s) outside 

 of the histidine region simultaneously confer 

 TRA-resistance and a relative intensitivity to 

 repression by L-histidine. (7) 



The site of repression is part of, or adjacent to, 

 gene G. Deletion of this "operator" region elim- 

 inates production of theenzymes by the histidine 

 genes. For example, mutant lusG-203 fails to 

 recombine only with the seven most terminal 

 sites of the G gene. Yet no histidine enzymes are 

 produced. Translocation of the remaining seven 

 structural genes into an episome, or further 

 deletion of genetic material to the "right" of the 

 histidine genes, allows return of coordinate gene 

 function which is, however, now unaffected by 

 the presence of L-histidine. W 



1. See Lee and Englesberg, Proc. Nat. Acad. 

 Sci., U.S. 48, 1962. 



1 . Ames and Hartman, In : The Molecular Basis 

 of Neoplasia, p. 322, 1962. 



2. R. G. Martin, J. Biol. Chem. in press, 1963. 



3. D. E. Sheppard and Hartman, Fed. Proc, in 

 press, 1963. 



4. Ames and B. Garry, Proc. Nat. Acad. Sci. 45, 

 1453, 1959. 



5. Ames and B. Garry, unpublished. 



6. A. P. Levin and Hartman, Bact. Proc, in 

 press, 1963. 



7. J. R. Roth, Ames and Hartman, unpublished. 



8. Ames, Hartman, and F. Jacob, J. Mol. Biol., 

 in press, 1963. 



4.8. Genetic Control of L-Histidine Biosynthesis in 

 Salmonella. Philip E. Hartman and Bruce N. 

 Ames (Bethesda, U.S.A.). 



Eight closely linked genes specify the structures 

 of eight proteins involved in L-histidine biosyn- 

 thesis. The gene order and the relative biochem- 

 ical steps are: £(2?), F(A), ,4(3), 7/(5?), 5(6 and 

 8), C(7), D(9), and G(l). A coding ratio of three 

 has been calculated for the complete genetic 

 region, about 1.3 x 10 4 nucleotide pairs long. W 



L-histidine and thiazole alanine feedback in- 

 hibit reaction 1 by altering the conformation of 

 the protein. ( 2 ) The sites of mutation in histidine- 

 excreting mutants with feedback-resistant en- 



4.9. Restoration of Operon Activity by Suppressors. 



J. R. Beckwith (London, Great Britain). 



The genes clustered in the Lac region of the 

 E. coli chromosome are under the control of a 

 single operator region adjacent to the gene for 

 (3-galactosidase. 0° mutants, located in this 

 region, prevent the synthesis of all three enzy- 

 matic activities associated with the operon, |3- 

 galactosidase (z), permease (y), and galactoside 

 transacetylase. It has been proposed that these 

 mutations prevent the transcription of messenger- 

 RNA from the operon. In this paper the iso- 

 lation and characterization of suppressors of an 

 0° mutant is reported. By the use of melibiose, 

 an cc-galactoside which requires permease but 



39 



