Section 4 — Gene action 



steps of these pathways are clustered; the thre- 

 onine deaminase gene lies outside that cluster. 

 A map of this segment of the B. subtilis genome 

 which bears the il-val and leu markers is being 

 constructed. 



Results of biochemical and genetic studies on 

 the regulation of these pathways will also be 

 presented. 



4.52. Non-genetic Control of Amino-acid Substitutions 

 in the Biosynthesis of the Antibiotic Polypep- 

 tide Tyrocidin. B. Mach (New York, U.S.A.). 



Tyrocidin is a decapeptide antibiotic known to 

 exist in three forms, A, B, and C, differing by 

 known single amino-acid substitutions involving 

 phenylalanine and tryptophan. The occurrence of 

 these forms might be under direct genetic control, 

 possibly as the result of mutations. However, 

 unlike the amino-acid replacements observed in 

 proteins, they might result from environmental 

 effects. 



The relative amount of the three forms of 

 tyrocidin synthesized by Bacillus brevis under a 

 variety of conditions, either by single bacterial 

 clones or by large volumes of culture, was deter- 

 mined after incorporation of C 14 amino-acids and 

 purification of the polypeptides. It was found 

 that the molecular forms of tyrocidin synthesized, 

 and therefore their specific amino-acid sequence, 

 depend on the availability of the amino-acids 

 involved in these substitutions. Variations in the 

 amounts of these amino-acids in the culture 

 medium result in drastic changes in the ratio of 

 tyrocidin A, B and C synthesized, and even in 

 the induced production of a new polypeptide, 

 tyrocidin D. 



Some aspects of this environmental control 

 over amino-acid substitution and its possible 



application to the biosynthesis of other types of 

 polypeptides will be discussed. 



4.53. The Colour and Fragrance in Plants and Their 

 Inheritance. John Politis (Athens, Greece). 



In 1911 we commenced a study of the forma- 

 tion of anthocyanin in plant cells, which up to 

 that time was unknown. 



In that paper we had shown that the antho- 

 cyanin in certain flowers first appear in the cyto- 

 plasm inside special corpuscles, which we had 

 named cyanoplasts. In geminating seedlings of 

 Raphanus sativus and other Cruciferae, antho- 

 cyanin is formed principally in the cells of the 

 subepidermal layer of the cotyledons and hypo- 

 cotyl axis. Each of these cells in its early stages 

 contains a nucleus, chloroplasts and a spherical 

 cyanoplast developing a red colour due to antho- 

 cyanin. 



The fact that the cyanoplasts often appear near 

 the nucleus and the fact that the colours of the 

 flowers as well as other substances (tannins, 

 chlorogenic acid, etc.) are inheritable characters, 

 led us to suggest that a cyanoplast is a gene, 

 escaped from the nucleus, and able to multiply 

 by budding and to produce anthocyanin. 



The fragrance of flowers and of other plant 

 parts is also an inheritable character. Researches 

 made by us on the glandular hairs of different 

 Labiatae and Compositae proved the concomit- 

 tant secretion of a bitter substance and an 

 essential oil. 



In order to explain the relation between the 

 above two substances as well as the transmission 

 of this inheritable character to the progeny, we 

 believe that a gene which comes out from the 

 nucleus is the cause of the production of a bitter 

 heteroside, from which through enzyme action 

 an essential oil is produced. 



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