96 M. R. Pollock 



Humphrey. J. H., and Lightbown, J. W. (1952). J. gen. Microbiol, 7, 



129. 

 Irwin, M. R. (1947). Advanc. Genetics, 1, 133. 

 KoGUT, M., Pollock, M. R., and Tridgell, E. J. (1956). Biochem. J., 



62, 391. 

 KossiKOV, K. V. (1950). Dokl. Akad. Nauk., USSR, 73, 381. 

 Lawrence, N. L., and Halvorson, H. O. (1954). J. Bad., 68, 334. 

 Lederberg, J., and Lederberg, E. M. (1952). J. Bad., 63, 399. 

 LiNZ, R. (1950). Ann. Inst. Pasteur, 78, 105. 

 Maas, W. K., and Davis, B. D. (1952). Proc. nat. Acad. Sci., Wash., 



38, 785. 

 Markert, C. L., and Owen, R. D. (1954). Genetics, 39, 818. 

 Owen, R. D., and Markert, C. L. (1955). J. Immunol., 74, 257. 

 Pollock, M. R. (1953). Symp. Soc. gen. Microbiol., 3, 150. 

 Pollock, M. R. (1956«). J. gen. Microbiol., 14, 90. 

 Pollock, M. R. (19566). J. gen. Microbiol., 15, 154. 

 Pollock, M. R., and Torriani, A. M. (1953). C.R. Acad. Sci., Paris, 



237, 276. 

 Pollock, M. R., Torriani, A. M., and Tridgell, E. J. (1956). Biochem. 



J., 62, 387. 

 Rogers, H. J. (1953). J. Path. Bad., 66, 545. 

 Saz, a. K., Weiss Brownell, L., and Slie, R. B. (1956). J. Bad., 71, 



421. 

 Saz, a. K., and Martinez, L. M. (1956). J. biol. Chem., 223, 285. 

 Sevag, M. G., and Gots, J. S. (1948). J. Bad., 56, 737. 

 Sneath, p. H. a. (1955). J. gen. Microbiol., 13, 561. 

 Stewart, B. T., and Halvorson, H. O. (1954). Arch. Biochem. Biophys., 



49, 168. 

 VouREKA, A. (1952). J. gen. Microbiol, 6, 352. 

 Yanofsky, C. (1952). Proc. nat Acad. Set., Wash., 38, 215. 

 YuDKiN, J. (1953). Nature, Lond., 171, 541. 



DISCUSSION 



Pontecorvo: The very important question that Dr. Pollock has raised, 

 of whether in gene mutations one can get qualitative changes, has been 

 in the minds of all of us for many years. Some years ago I would have 

 agreed with him that they were mainly quantitative, but the fact that 

 out of not more than ten cases which have been properly studied, one 

 (i.e. tyrosinase) is of that kind is more than I would have expected. 



Pollock: I don't think a thermostability change is at all a good 

 criterion. 



Pontecorvo: It is a difference in the enzyme itself. 



Pollock: No, I don't think this is necessarily so. I think it could be 

 due to association with some other molecule, which changes its thermo- 

 stability. You can get changes like that, as Halvorson has shown with 

 enzymes derived from spores. There is a profound change in thermo- 

 stability, which seems to go hand in hand with solubilization of the 



