426 



D. M. BROWN AND A. R. TODD 



"inner esterified" nucleotides in ribonuclease digests. The evidence for this 

 suggestion, however, rested on the disparity between the number of acidic 

 functions Uberated by the enzyme in relation to the conclusion, now known 

 to be erroneous, "2 that the products were all mononucleotidic. 



•0 



OH OPO3H2 



CH2-0H 



RNase 0=^ 



*' N 



CH-H — h 

 I H H 



N. 



H 



■CH,-OH 



NHo 



NH, 



alkali 



■0- 



CHj-OH 



RNase 



N, 



CH- 



I 



N. 



OH OPO3H2 



■CH,-OH 



H H 



H 



OH 



Markham and Smith"^ have studied the oligonucleotide fragments in 

 ribonuclease digests by paper chromatographic and paper electrophoretic 

 techniques, thereby separating a variety of di- and trinucleotides. They 

 found that during the rapid initial action of the enzyme substances were 

 produced which were then transformed more slowly into the oligonucleo- 

 tides without change in the gross analytical composition (base-phosphorus 

 ratio). They suggested, on the basis of the hydrolytic mechanism advanced 

 by Brown and Todd,®^ that these initially produced substances carried a 

 cyclic 2',3'-phosphoryl group on the terminal (pyrimidine) nucleoside 

 residue; further action of the enzyme on these cyclic groups then yielded 

 the true oligonucleotides. Brown, Dekker, and Todd^°^ pointed out that 

 this latter process, being analogous to that studied in their work on the ac- 

 tion of ribonuclease on cyclic phosphates of uridine and cytidine, should 

 yield oligonucleotides bearing a terminal 6 (3') -nucleotide residue, and 

 hence that on alkaline hydrolysis pyrimidine h nucleotides would be pro- 

 duced from them. In agreement with this view, Volkin and Cohn^^ found 



"2 Inter al., G. Schramm, W. Albrecht, and K. Munk, Z. Naturforsch. 7b, 10 (1952). 

 "3 R. Markham, and J. D. Smith, Biochem. J. 52, 558 (1952). 



