THE SYNTHESIS OF NEW SUBSTANCES 381 



valine (Bonner 1946). Another type of interaction is exhibited by the 

 fact that in certain strains of Neurospora and Aspergillus which require an 

 external source of L-arginine, an addition of L-lysine to the medium 

 reduces the effect of the added arginine; and the same competitive in- 

 hibition between the two substances is shown by a lysine-requiring strain 

 (cf. Pontecorvo 1950, Emerson 1950). 



Finally, we may quote from another field a biochemical example of 

 competition between gene-produced substances (or, less probably, the 

 genes themselves) for a common substrate. One of the earliest attempts to 

 link up gene action with known chemical compounds was the investiga- 

 tion of the genetic control of flower colour (Lawrence and Price 1940, 

 Haldane 1941, 1954). Genes were identified which caused various pre- 

 cisely known chemical changes in the constitution of the coloured sub- 

 stances. Probably these genes act by controlling the formation of enzymes; 

 the evidence is no better, and not much worse, than it is for the similar 

 hypothesis in the Neurospora work. Now in crosses involving a number of 

 genes affecting the various different classes of pigments (anthocyanins, 

 flavones and chalkones) it was found that there were interactions in which 

 all the different types of substance were involved. When much antho- 

 cyanin was formed, this led to a reduction in the amounts of flavone and/ or 

 chalkone. Thus the different gene-activities competed, with efficiencies 

 corresponding to the number and strength of the genes involved, for a 

 limited amount of a common substrate from which the compounds of all 

 those types were derived (Lawrence 1950). 



5. The synthesis of proteins 



Since most, if not all, enzymes are proteins, the evidence from genetics 

 that genes control the formation of enzymes should be linked with such 

 general information as we have about the synthesis of proteins in cells. 

 Although the nature of the chemical processes involved in this synthesis 

 is still almost entirely obscure, there is quite a large amount of rather 

 indirect evidence on the role which various parts of the cell structure play 

 in the production of proteins. Most of this does not come from in- 

 vestigations which have used embryos as the experimental material (for 

 which see ten Gate 1953 and Gustafson 1952) but from studies in the 

 general field of biochemistry and physiology. 



It is, in the first place, fairly generally agreed that the nucleic acids 

 participate in an important manner in protein synthesis and indeed are 

 probably essential for it. The synthesis of new chromosomal proteins, 

 which is involved in the reduphcation of the genes before cell division 



