THE CHEMICAL COMPOSITION OF STRAINS OF TOBACCO MOSAIC VIRUS

There is a striking similarity between the properties that have been found for the viruses that have been isolated in the form of high molecular weight nucleoproteins and the properties that have been ascribed to genes (Muller, 1935; Demerec, 1939; Stanley, 1940). As may be seen from Figure 1, one estimate of the approximate size of a gene would place it in the midst of the viruses, many of which are larger and many of which are smaller. Both viruses and genes may be regarded as large nucleo-proteins that have the ability to perpetuate themselves by reproduction within, and only within, certain specific living cells. Both may undergo sudden changes either spontaneously or as a result of irradiation, and these changes are then faithfully reproduced in subsequent generations. Although it has not proved possible to isolate and study genes in vitro without loss of their viability, in the case of...