24 



MAURICE J. BESSMAN 



TABLE IX 

 Incorporation of Single Deoxynucleotides into DNA" 



Additions'" 



DNA-P32 



(m/xinoles) 



dCTP + dGTP + TTP + dATP 



dCTP + dGTP 4- TTP 



dCTP + dGTP 



dCTP 



dCTP (DNA omitted) 



3300 



15.7 



5.1 



2.5 



0.0 



" From Kornberg (1959). 



* The incubation mixture (0.3 ml) contained 5 mAimoles of dCP^'PP (7.1 X 10' cpm 

 per ^raole), and of the other deoxynucleoside triphosphates where indicated, 1 yumole 

 of MgClo, 20 /xmoles of glycine buffer, pll 9.2, 10 fxg of DNA, and 3 ng of enz\'me frac- 

 tion \T. The incubation was carried out at 37 °C for 30 minutes. 



of the radioactivity is released before appreciable amounts of the DNA 

 has been rendered acid-soluble (Fig. 7). Since this enzyme has been 

 shown to hydrolyze polynucleotides (ribo- and deoxyribo-) in a stepwise 

 fashion starting from the nucleoside end (Laskowski et al., 1957; Bow- 

 man, 1957; Khorana et al., 1958; Singer et al., 1958), it would appear 



lOOn 



60 

 Time in Minutes 



Fig. 7. Action of venom i)hosijhodiesterase on limit product. (From Adler et al., 

 1958.) 



that the added deoxyribonucleotides are localized at the ends of the 

 DNA chain. On the average, one deoxyribonucleotide is added per DNA 

 chain. It may be asked whether each of the deoxyribonucleotides 

 is added to specific DNA chains terminating with a specific base or 

 whether dCTP for example will add to DNA chains terminating in 

 any of the deoxyribonucleotides. Results of nearest neighbor analyses 



