Wild T ype 



Homocysteine 



CH2-SH 



CH2 

 "^ CH-NHz 



COOH 



Methionine 

 CH2-S-CH3 



CH2 



CH-NH2 



COOH 



COOH 



^-Aminobenzoic 

 acid 



GROWTH 



CH3 

 ^CHOH 



CH-NH2 

 COOH 



Threonine 



Sulfonamide Requirin g, Homoc v steineless 



H-9a 



*- .»-.■■- 









•- c?/f(yr ^ 



Fig. 12.5— 

 by genes of 



CH3 



CHOH 



CH-NH2 



COOH 



Certain biochemical reactions essential to growth in Neurospora as influenced 

 the sulfonamide-requiring strain (E-15172), the homocysteineless strain (H-98), 

 and the aminobenzoicless strain (1633). 



208 



