428 



D. M. BROWN AND A. R. TODD 



represented in the scheme as applying to a straight-chain polynucleotide, 

 they are equally readily accommodated on branched-chain structures 

 which fulfil the conditions laid down on the basis of the results of chemical 

 hydrolysis (p. 422). 



Py-Cj. Pu-Ca- Py-Cr Py-Cz- Pu-Cj- 





Ca- Ca- Cs- Cs- 



I ^P I ^P ^P I ^P 

 C^. C5. C5. C5. 



.^ 



Pu-C2- Py-Cz-. 



OH 





Pu-Ca- Py-Ci 



RNase (rapid) 

 ^0 Py-C2; 



RNase (slow) 



I 



Py-Cr 



>^ 



PU — Cy 



OH 



r 



\i 



Co-OPOsHs 



C3-OP03Hj 



C,. 



prostate phospliatase 



Pu-C2- Py-C2.-0H Py-Cj-OH 



alkali 



1 



Pyrimidine b nucleotides and 

 purine a+b nucleotides 



a. 



C,.-OH 



C,.-OH 



Cfi. 



C5.-OH 



J 



periodate 



Oxidation products 



Purine nucleotides and 

 pyrimidine nucleosides 



6. Structure of Oligonucleotides Derived from Ribonucleic Acids 



That the general stucture of the oligonucleotides present in ribonuclease 

 digests is correct seems clear from the degradations described above. Their 

 chemistry appears to be wholly consistent with the requirements set out by 

 Brown and Todd^^ f^om their discussion of chemical hydrolytic mechanisms. 

 It is unfortunate that up to the present, no oligonucleotides have been 

 isolated in substance, apart from the compounds obtained by Merrifield 



