96 NUCLEIC ACIDS AND NUCLEOPROTEINS 



transmitted. Compositional regularities in themselves are not suf- 

 ficient for an explanation; but they will, I believe, have to be 

 taken into account in any eventual solution of this problem. You 

 may not be able to reconstruct an animal from its tracks; but you 

 may succeed in identifying it through its footprints. 



7. REMARKS ON NUCLEOPROTEINS 



During my entire talk this evening, there has loomed in the 

 background, without ever making a real appearance, the second 

 half of my title, the nucleoproteins. Immanently, they must be 

 present in all our thinking on nucleic acids, for there is little evi- 

 dence that nucleic acids occur in the free state in the living cell. 

 If they ever disrobe, it is only temporarily; for the most part they 

 appear dressed decently in a coat of protein. Why not, therefore, 

 consider the whole thing, the conjugated proteins; the more so 

 since there is much evidence of the close connection between 

 nucleic acid and protein synthesis? In reality, we are not ready 

 for it despite the merry voices of innumerable biochemical boy 

 scouts who have pitched their hasty tents all over the field. 



But it is probably not an accident that nucleic acids and 

 proteins are so closely associated in nature. It is hard to believe 

 that the proteins, in all their variety, have only the function of 

 an ornament or wrapping material. Even in the plant viruses, I 

 do not find it easy to entertain the Cytherean vision of a nucleic 

 acid resting in a merely protective shell of protein. 



I have no time to go into all that and can only refer to a few 

 recent discussions^^- *^-^'^. But I should like to repeat one sugges- 

 tion^^, namely, that the regularity in PNA, and perhaps also in 

 DNA, of which I have spoken, 6-Am = 6-K, could be imposed 

 by an extended polypeptide chain bonded to two polynucleotide 

 chains so that each peptide carbonyl is linked by a hydrogen bond 

 to the 6-amino group of adenine or cytosine and each peptide 

 amino group to the 6-keto group of guanine or uracil. It is rather 

 unhkely that such nucleoproteins will be found easily^^; the en- 

 forcement of this stoichiometry may be an essentially dynamic 



