. Cell heredity. Cytogenetics. MUTATION AS A CHEMICAL PROCESS 227 the protein in the mature phage. It is known to consist of many en- zymes, some of which are directly involved in the polymerization of DNA. The requirement of protein for DNA synthesis is not restricted to cases such as phage development where the DNA is of a new sort not previ- ously synthesized by the bacterium. The synthesis of any DNA seems to require the synthesis of a protein peculiar to it, either concomitantly, or preceding it. When thymineless-histidineless (thy~ his~) bacteria are starved for thymine but supplied with
. Cell heredity. Cytogenetics. MUTATION AS A CHEMICAL PROCESS 227 the protein in the mature phage. It is known to consist of many en- zymes, some of which are directly involved in the polymerization of DNA. The requirement of protein for DNA synthesis is not restricted to cases such as phage development where the DNA is of a new sort not previ- ously synthesized by the bacterium. The synthesis of any DNA seems to require the synthesis of a protein peculiar to it, either concomitantly, or preceding it. When thymineless-histidineless (thy~ his~) bacteria are starved for thymine but supplied with histidine, essentially no DNA but a good amount of protein is synthesized. Upon transfer of such thymine- starved bacteria into a medium containing thymine, but now no histidine, protein synthesis ceases but abundant DNA synthesis begins (Figure ). Was the previous synthesis of protein required for the formation of DNA? Prevention of the initial protein synthesis during thymine starvation by chloramphenicol shows that it was. For, when these bac- teria are transferred to medium with thymine but with no histidine or chloramphenicol, protein synthesis still does not take place. Further- more, the vigorous synthesis of DNA observed in the first instance does not take place; only a minimal synthesis characteristic of cells that have not been starved for thymine is observed. The new synthesis of protein during thymine starvation was required for the excess DNA that formed when thymine was subsequently provided. Some studies with ultraviolet light similarly implicate protein in the process of DNA replication and in the process of mutation as Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Sager, Ruth; Ryan, Francis J. (Francis Joseph), 1916-. New York, Wiley
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