426 CHAPTER 46 



SUMMARY AND CONCLUSIONS 



DNA has a function other than self-replication. This additional function is clearly de- 

 pendent upon its sequence of nucleotides. In terms of this additional capacity, DNA cistrons 

 can be classified as being genes for structure and/or genes for function. 



When acting as a gene for function, the cistron serves as an operator that controls the 

 expression of structural genes which are its linear neighbors, the whole complex of genes 

 comprising an operon. It is speculated that the operator gene may produce its different 

 effects by sharing and not sharing nucleotides with structural genes in the operon. 



REFERENCES 



Gorini, L., "Antagonism Between Substrate and Repressor in Controlling the Formation 

 of a Biosynthetic Enzyme," Proc. Nat. Acad. Sci., U.S., 46:682-690, 1960. 



Hartman, P. E., Loper, J. C, and Serman, D., "Fine Structure Mapping by Complete Trans- 

 duction Between Histidine-Requiring Salmonella Mutations," J. Gen. Microbiol., 

 22:323-353, 1960. 



Jacob, F., and Monod, J., "Genetic Regulatory Mechanisms in the Synthesis of Proteins," 

 J. Mol. Biol., 3:318-356, 1961. 



Jacob, F., Perrin, D., Sanchez, C, and Monod, J., "The Operon: A Group of Genes Whose 

 Expression Is Coordinated by an Operator" (in French), C. R. Acad. Sci., Paris, 

 250:1727 1729, 1960; translated and reprinted in Papers on Bacterial Genetics, 

 Adelberg, E. A. (Ed.), Boston, Little, Brown, 1960, pp. 395-397. 



McClintock, B., "Some Parallels Between Gene Control Systems in Maize and in Bacteria," 

 Amer. Nat., 95:265-277, 1961. 



Yanofsky, C, and St. Lawrence, P., "Gene Action," Ann. Rev. Microbiol., 14:311-340, 1960. 



QUESTIONS FOR DISCUSSION 



46.1. How does the phenotypic effect of o" differ from that of its alleles, o+ and o-? 



46.2. How does an operator gene differ from a regulator gene? 



46.3. Do you suppose the nucleotide sequence is longer in an operator gene than it is in the 

 other genie members of an operon? Why? 



46.4. Does prophage act as one or more regulator genes? Explain. 



46.5. Some workers classify genes into three kinds: those for structure, for regulation, and 

 for operation. Do you believe this distinction is basic? useful? Explain. 



46.6. Hypothetically, what kinds of phenotypic effects might operons produce in man? 



46.7. Discuss the hypothesis (of J. F. Danielli) that the nucleus controls the possibility of 

 particular chemical substances appearing in cells, while the cytoplasm controls the 

 way in which macromolecules are organized into functional units. 



46.8. In what ways do genes function? 



46.9. What is your present concept of the cistron? 



3m-<\ 



