AVERY, MACLEOD, MCCARTY 



discover and maintain x-ray induced 

 mutant strains which are character- 

 ized by their inability to carry out 

 specific biochemical processes. 



Follow ing this method, three mutant 

 strains have been established. In one 

 of these the ability to synthesize vita- 

 min Be has been wholly or largely lost. 

 In a second the ability to synthesize 

 the thiazole half of the vitamin Bi 

 molecule is absent, and in the third 

 para-aminobenzoic acid is not syn- 

 thesized. It is therefore clear that all 

 of these substances are essential growth 

 factors for Neurospora}^ 



Growth of the pyridoxinless mutant 

 (a mutant unable to synthesize vitamin 

 Be) is a function of the Be content of 

 the medium on which it is grown. A 

 method is described for measuring the 

 growth by following linear progres- 

 sion of the mycelia along a horizontal 

 tube half filled with an agar medium. 



Inability to synthesize vitamin Be is 



173 



apparently differentiated by a single 

 gene from the ability of the organism 

 to elaborate this essential growth sub- 

 stance. 



Note: Since the manuscript of this 

 paper was sent to press it has been 

 established that inability to synthesize 

 both thiazole and aminobenzoic acid 

 is also inherited as though differen- 

 tiated from normal bv single genes. 



Work supported in part by a grant 

 from the Rockefeller Foundation. The 

 authors are indebted to Doctors B. O. 

 Dodge, C. C. Lindegren and W. S. 

 Malloch for stocks and for advice on 

 techniques, and to Miss Caryl Parker 

 for technical assistance. 



11 The inference that the three vitamins 

 mentioned are essential for the growth of 

 normal strains is supported by the fact that 

 an extract of the normal strain will serve as a 

 source of vitamin for each of the mutant 



Studies on the Chemical Nature of the Substance 

 Inducing Transformation of Pneumococcal Types 



Induction of Transformation by a Desoxyribonucleic 

 Acid Fraction Isolated from Pneumococcus Type III 



OSWALD T. AVERY, COLIN M. MACLEOD, 

 and MACLYN MCCARTY 



Reprinted by authors' and publisher's permis- 

 sion from Journal of Expermiejital Medicine, 

 vol. 79, 1944, pp. 137-158. 



This paper is indicative of one of the curre?it tre?jds in genetics, 

 which has developed niaiiy divergent pathways. The reader who has 



