132 H. GOBIND KHORANA 



(Under suitable conditions, good rates of exchange of the terminal phos- 

 phate group of GDP with the phosphate in the medium have also been ob- 

 obtained with the purified E. coli enzyme. 60a ) 



There are other factors which make the enzymic reaction much more 

 complex than it might appear at first sight. These factors stem from the 

 metal requirement of the reaction. Of the three reaction components in- 

 volved, a primer, nucleoside diphosphate, and an enzyme, one or more may 

 be required as the metal complex. 



It is clear that a prerequisite for an attack on some of these questions is 

 the availability of a completely pure enzyme. 



/. Distribution of Polynucleotide Phosphor ijlase 



In addition to the sources mentioned above, the occurrence of the enzyme 

 has been established in extracts of a number of bacterial species. 61 A small 

 activity was found in spinach leaf extracts. 61 Net phosphoro lysis of enzymi- 

 cally synthesized polyadenylic acid by a fraction from guinea pig liver 

 nuclei has been reported but as yet net synthesis of polynucleotide has not 

 been demonstrated. 62 



An enzyme has been purified from yeast, which, like the polynucleotide 

 phosphorylase, catalyzes a rapid exchange between labeled orthophosphate 

 and the terminal phosphate groups of the ribonucleoside-5'-diphosphates, 

 but does not phosphorolyze any polynucleotides prepared by the use of 

 the bacterial enzymes, nor does it catalyze polymer formation. 63 



g. Summary of the Types of Oligo- and Polynucleotides Made Available by 

 Polynucleotide Phosphorylase 



The discovery of polynucleotide phosphorylase has made available a 

 variety of polynucleotides which in turn have made possible many physico- 

 chemical and enzymic studies of polynucleotides. Further, a variety of 

 oligonucleotides has become available by the combined use of polynucleotide 

 phosphorylase, and other enzymes. While the total range and number of 

 polymers available will no doubt be enlarged, the main types that have 

 already been prepared are listed in Table I. 



3. Ribonucleoside-5'-Triphosphates as Precursors of 

 rlbopolynucleotides in mammalian systems 



a. Incorporation of Ribonucleoside-5' -Phosphates into Ribonucleic Acids 



The studies on the acid -soluble nucleotide pools of a variety of tissues by 

 Potter and co-workers 30 and on the incorporation of labeled nucleotides 



60a M. Grunberg-Manago, R. J. Hilmoe, M. F. Singer, and L. A. Heppel, in press. 



61 D. O. Brummond, M. Staehelin, and S. Ochoa, J. Biol. Chem. 225, 835 (1957). 



62 R. J. Hilmoe and L. A. Heppel, J. Am. Chem. Soc. 79, 4810 (1957). 



63 M. Grunberg-Manago and A. del Campillo-Campbell, unpublished results (1959). 



