184 Discussion 



specific nucleases, whatever they may be. The heterogeneity, in many 

 different ways, of nucleic acids is rapidly becoming apparent; hetero- 

 geneity according to site, as Prof. Davidson could attest; to metabolic 

 activity in a specific site; to size. I am reminded of an observation 

 coming from Dr. Markham's laboratory with respect to 5' ends in nucleic 

 acids and particularly in tobacco mosaic virus. The evidence of these 5' 

 ends depends on how you precipitate the virus. If you do it one way 

 you get evidence of 5' ends, if you do it another way you do not. Here 

 is an apparent heterogeneity in terms of size or structure or admixed 

 material which appears to depend on the method of precipitating the 

 virus from the plant extract. Dr. Gale's evidence indicates that some- 

 thing (probably non-nucleotide as he himself says) which is carried by 

 nucleic acids has a pronounced effect, an effect in which we are all 

 interested. But in interpreting these effects we must remember that in a 

 preparation of RNA and DNA the major component may indeed be 

 what the letters stand for, but there is no guarantee that that is all that 

 is present in the preparation. 



Bracket: Dr. Gale said that, as a rule, intact cells are not permeable to 

 nucleic acids. I think that the nucleic acids, at any rate when they are 

 not very highly polymerized, can get into certain cells. They certainly 

 can get into the amoebae. RNA can also get into the cells of the onion 

 root : cytological evidence shows that it first produces extensive mitotic 

 activity, followed by an inhibition. Most people still believe, and I 

 believed up to two years ago, that a large molecule like a nucleic acid 

 would not penetrate into a cell. I now think that we can no longer 

 accept that this is always true. 



With regard to the question of the possible role of copper, has copper 

 any effect on RNA and protein metabolism, producing for instance a 

 dissociation of the two? It has been found that there may be an 

 accumulation of RNA in bacteria treated with cobalt under conditions 

 where growth stops; I wonder whether copper can produce such an 

 effect. 



Gale: A dissociation of protein synthesis and nucleic acid synthesis 

 has been shown with cobalt, but not, as far as I know, with copper. In 

 the glycine incorporation system cobalt will antagonize the toxic action 

 of copper, but whether or not this is due to differences in the affinity of 

 their chelating systems, I don't know. 



