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GENETIC AND BIOCHEMICAL STUDIES ON ISOLEUCINE AND VALINE REQUIRING MUTANTS OF ESCHERZCHZA COLZ

N microorganisms, a single mutation event can result in the growth require’ ment of two amino acids, isoleucine and valine. This is not considered unusual since the two amino acids share a common biosynthetic pathway (UMBARGER and DAVIS 1962), (Figure 1). In Salmonella typhimurium (GLANVILLE and DEMEREC 1960), the genes controlling the synthesis of the enzymes of the isoleucine-valine pathway are clustered in a short region of chromosome. On the other hand, the genes of Neurospora crassa ( KIRITANI 1962; WAGNER, BERGQUIST, BARBEE and KIRITANI 1964) and Saccharomyces cerevisiae (KAKAR and WAGNER 1964) that control the production of similar enzymes are not clustered in any one region of a chromosome. The finding of what may be organizational mutants in Neurospora (WAGNER, KIRITANI and BERGQUIST 1962) and Saccharomyces (KAKAR and WAGNER 1964) provides a clue with which one can analyze the relationship between the cytoplasmic organization of enzymes of the biosynthetic pathway and the location of the genes controlling these enzymes. A study of the