On the Species Specificity of the 

 Nucleic Acids of Bacteria 



A. N. BELOZERSKIÏ 



A. N. Bakh Institute of Biochetnistry, U.S.S.R. Academy of Sciences, 

 and Faculty of Biology and Soil Science, Moscow State University 



In recent years our concepts of the specificity of the nucleic acids have under- 

 gone considerable changes. Whereas before there were no reasons for con- 

 sidering nucleic acids as highly specific substances, somewhat resembling pro- 

 teins in this respect, now the situation is radically different. The need for this 

 reappraisal was brought out most strikingly by the remarkable investigations of 

 Professor Chargaff 's laboratory. These investigations made it abundantly clear 

 that deoxyribonucleic acid (DNA) from different biological sources differs in 

 purine and pyrimidine contents. The work of this laboratory, coupled with 

 certain other data, was also highly important because it provided a substantial 

 stimulus to study the structure of nucleic acids, since it became obvious that the 

 theory of the tetranucleotide structure of nucleic acids, formulated earlier in its 

 final form by Levene, did not ally with the new experimental findings. 



Furthermore, the new data on the structural chemistry of the nucleic acids 

 revealed a non-uniform nucleotide distribution both in ribonucleic acid (RNA) 

 and in DNA, which furnished grounds for assuming a possible and even far- 

 reaching isomerism in this group of compounds. 



Nevertheless, if the results of work on the specificity and heterogeneity of the 

 nucleic acids are brought together, we may speak of the following possible types 

 of specificity of the nucleic acids: (i) species specificity, (2) age specificity, (3) 

 organ and tissue specificity, (4) organoid specificity, and finally, (5) molecular 

 specificity, in which case, for example, the same cell organoid can contain a 

 series of different molecules of nucleic acids [i]. 



For a final solution of the problem of the reality of these types of nucleic acid 

 specificity it is necessary to accumulate far more experimental information. 

 Whereas with respect to DNA the question of species specificity — and perhaps 

 molecular specificity — can be considered in some degree answered, with respect 

 to RNA there are few data and even these are often contradictory, this being 

 due to the fact that RNA appears to be highly labile and its isolation from cells 

 or tissues subjects it to a greater or lesser degree of degradation. At any rate in 

 the first stage of investigations in this field it is particularly important to estab- 

 lish species specificity for both DNA and RNA. This is all the more important 

 in view of the genetic role attributed to DNA, while RNA is believed by a number 

 of investigators to be one of the decisive factors responsible for the specific 

 distribution of the amino acids in the peptide chain that is formed. 



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