ADAPTATION TO PANTOTHENATE DEFICIENCY 



22-4 



non- synthesizing nuclei, the more effective they are in inhibiting 

 the synthesizing nuclei. Hence, in a high concentration of leucine 

 there is a very large number of leucineless nuclei, so that if a mu- 

 tation to synthesizing ability did occur, it would be effectively sup- 

 pressed, while if one occurred in a smaller number of leucineless 

 nuclei (at the lower leucine concentration) the mutation would not 

 be effectively suppressed and adaptation would occur. 



This selection phenomenon is sufficient to explain the increase 

 in number of adaptations on lower concentrations of leucine. It is 

 impossible, however, to determine whether the concentration of 

 leucine affects the mutation rate because of the competition between 

 the nuclei. 



The above studies show that random mutation and selection by 

 the environment can account for some adaptations but the evidence 

 does not exclude other possibilities, particularly the possibility of 

 non-random induction of mutation by specific agents. In the experi- 

 ments of Luria and Delbruck (1943) it was not possible to determine 

 the mutation rate in the presence of the phage because of the lethal 

 action of the phage; in Ryan's (1946) work, competition between the 

 nuclei prevented study of the rate of occurrence of mutations in the 

 presence of various concentrations of leucine. 



Specific induction of mutations by external agents is a possi- 

 bility which must be considered, for various workers, particularly 

 Avery and Biovin, have demonstrated what may be transformation 

 of certain types of pneumococci and Escherichia coli into other types 

 by the specific action of desoxyribose nucleic acid extracts. 



SLOW ADAPTATION TO THE ABSENCE OF 



PANTOTHENATE BY A PANTOTHENATELESS 



MENDELIAN RECESSIVE 



Lindegren and Raut (1947a, b) studied a haploid pantothenate - 

 dependent strain of Saccharomyces cerevisiae which adapted to pan- 

 tothenate independence in about ten days when inoculated into medium 

 to which no pantothenate had been added. The time required for ad- 

 aptation was shortened by the addition of minute amounts of panto- 

 thenate, but was prevented entirely by the addition of larger amounts 

 of pantothenate. The regularity of occurrence of adaptation and its 

 correlation with increases in small amounts of pantothenate were 

 interpreted to indicate induction of adaptation by pantothenate. How- 

 ever, it was pointed out that the data did not exclude the possibility 

 of selection of infrequently occurring mutants. 



They compared the growth curves of genetically different yeasts 

 in media containing different concentrations of pantothenate. Various 

 members of the pedigree are shown in Table 20-2 with the following 

 amounts of pantothenate added per liter: 100, 50, 20, 10, 5, 2, 1, 0.5, 



