HALL AND DOTY 



33 



molecule as its counterions become further removed from it. Upon the addi- 

 tion of salt the viscosity returns to a low value, showing the reversibility of 

 the effect. Thus the solution properties of the RNA are found to be satisfac- 

 torily correlated with a randomly coiled, single-chain structure. 



THE HYPOCHROMICITY OF RNA 



In view of the substantial nucleotide attractions that appear to be necessary 

 to account for the relatively tight coiling of RNA in 0.01 M phosphate buffer 

 we sought to examine the possibility that hydrogen bonds between pairs of 

 nucleotides were present in a random fashion within each coiled RNA mole- 

 cule. Since the break-up of hydrogen bonds between base pairs in the denatura- 

 tion of deoxyribose nucleic acid is accompanied by a substantial rise in ultraviolet 

 absorbance [8], it seemed reasonable to look for the same effect in RNA. The 

 hydrogen bonds that may exist in RNA would be broken during the expansion 

 that was seen to accompany the removal of salt from the RNA solution. Alter- 

 natively such hydrogen bonds may be expected to be broken with increasing 

 temperatures, as occurs with deoxyribose nucleic acid. We have combined these 

 two hydrogen-bond-breaking effects by measuring the optical density of RNA 

 solutions at 258 mu as a function of temperature at various ionic strengths. 



The results of this study are shown in figure 5. It is seen that in 0.01 M 



675 



.650- 



.625 



.600 - 



.575 



0.2 4 6 



RNA CONCENTRATION, gms/lOOcc 



Fig. 4. Reduced specific viscosity of 

 RNA in water; dependence on concen- 

 tration. 



100 



Fig. 5. Variation of the optical density of 

 RNA solutions at 258 m« with temperature and 

 ionic strength. 



