TABLE VI 



Concentration Dependence of Chemical Shifts for Cytidlne, Thymidine, and Uridine 



Protons at 35° ^' "^ 



0.35^ 



111.8 



111.8 



^'* 0.0 



457.5 

 456.9 



+0.6 



376.4 



373.9 



+2.5 



B. Thymidine 



141.8 

 139.8 

 +2.0 



268.3 



267.3 



+ 1.0 



241.2 



239.2 



+2.0 



226.4 



224.2 



+2.2 



228.7 

 228.7 



0.0 



H-5 



H-b 



H-1' 



H-2' 



H-3' 



H-4' 



H-5' 



H-5" 



— Solvent- D^O. Numbering of the nucleoside atoms shown, _e .^ . , with cytidine and thymidine. 



— ConcentraL ions approaching limits of solubility. 



S. From Schweizer, Chan and Ts'o, J. Am. Chera. Soc . 87 , 5241 (1965); reproduced with 

 permission of the American Chemical Society. 



cytidine 



thymidine 



dinucleotides has been made successfully in 

 our laboratories. Hopefully, this approach can 

 be applied to small nucleic acids such as 

 transfer RNA (6). More complete description 

 and discussion of these studies can be found 

 in the original papers published from our lab- 

 oratory. Nevertheless, sufficient data have been 

 presented here to indicate the tendency for the 

 bases and nucleosides in water to stack up 

 vertically with the heterocyclic rings in a 

 partial overlapping fashion. We are now ready 

 to go to the next step of complexity. 



The simple system of monomer-monomer 

 interactions can be studied quantitatively by 

 thermodynamic and spectroscopic methods. 

 However, the system does not have the specifi- 

 city exhibited at the level of polymer-polymer 



interaction. Consequently, we turn our attention 

 to the nucleic acid interaction at the polymer- 

 monomer level. A model system for this kind 

 of study should have the following characteris- 

 tics: 



1. The polymer should have a minimal 

 degree of self-interactions. 



2. Solubility of both polymer and monomer 

 should be sufficiently high. 



3. The electrostatic forces shouldbe mini- 

 mal. 



4. Its properties are relevant to those of 

 a well-characterized polymer-polymer 

 interaction system. 



The above criteria are apparently met by 

 the system: poly uridylic acid and adenosine 

 (7). The binding of adenosine to poly Uwas first 



189 



