222 Cytoplasm as Seat of Genetic Properties 



entrance of the virus into the germ cells leads to situations which sim- 

 ulate heredity in some respects. Still, I am unable to see that cytoplas- 

 mic heredity in any sense is involved, unless the facts might be 

 advocated as demonstrating an evolutionary step that leads from an in- 

 fectious virus to the establishment of a plasmagene. The legitimacy of 

 the latter speculation may be accepted or doubted. 



It was Muller who, after d'Herelle's discovery of the bacterio- 

 phage, first suggested the idea that viruses are a kind of free living 

 genes. But only after Stanley's work, proving one virus to be a nucleo- 

 protein molecule (RNAI) visible and measurable in the electron 

 microscope, did the comparison between virus and gene become 

 popular. The reasons for the comparison are, of course, self-duplica- 

 tion, nucleoproteinic nature, and dependence upon a substrate. There 

 can be no doubt that a comparison of bacteriophage with genes is 

 wrong, since we know that the phage is an organism with a genetic 

 structure which permits linkage and crossing over. Thus only the virus 

 proper remains as a basis for the speculations maintaining that there 

 is no difference between a virus and so-called plasmagenes, since all 

 transitions are supposed to exist. The genoids of L'Heritier and the 

 kappa particles are supposed to be such particulates, which we might 

 call viruses or plasmagenes equally well. The main reason for such 

 assumptions is that these cytoplasmic parasites or symbionts are con- 

 trolled in their existence, number, and properties by genetic con- 

 ditions of the host nucleus. It is overlooked, when such a conclusion is 

 drawn, that all chemical, physical, and antigenic properties of the 

 cytoplasm are under nuclear control. Since the cytoplasm is the en- 

 vironment for these parasites, anything that influences the environ- 

 ment, including normal or mutant loci in the nuclear genie material, 

 may also affect the behavior of the parasites. The behavior of the 

 tubercle bacillus is in some ways controlled also by the constitution, 

 that is, the genetic makeup, of the host. 



b. So-called cytoplasmic mutation in yeast 



Ephrussi et al. (reviews and literature, 1950, 1951, 1953) have 

 analyzed a "mutation" in yeast which results in the appearance of 

 small colonies due to a respiratory deficiency: namely, the inability of 

 the mutant cells to synthesize cytochrome oxidase (and other respira- 

 tory enzymes). Yeast may thrive on respiration in the presence of 

 oxygen or on glycolytic fermentation in its absence. In the small 

 mutant, cyanide-sensitive respiration is suppressed. The enzymatic 

 details have been worked out by Slonimski (1952). An important 



