31. SYNTHESIS OF POLYNUCLEOTIDES 141 



/. The Limited Synthetic Reaction 9 ' 1 



Although maximal synthesis by the polymerase requires the complement 

 of four deoxyribonucleoside-5'-triphosphates, a very limited reaction has 

 been noted when only one of the triphosphates is present. The extent of 

 this reaction is only about one-thousandth of that of the complete reaction 

 and has been shown to result in the addition of a single or sometimes runs 

 of a few nucleotide units to those ends of the primer DNA chains which 

 bear 3 '-hydroxy 1 groups. The conclusion that the incorporated deoxyribo- 

 nucleotides were indeed in 5'-3' phosphodiester linkage with primer DXA 

 was established by carrying out the limited reaction in the presence of a 

 single deoxyribonucleoside-5 '-triphosphate isotopically labeled in the inner- 

 most (stable) phosphate group. Degradation of the product, by the micro- 

 coccal deoxyribonuclease 93 followed by spleen phosphodiesterase, 94 to deox- 

 yribonucleoside-3 '-phosphates released the labeled phosphate group in each 

 of the nucleoside-3 '-phosphates. The location of the incorporated nucleo- 

 tides at or near the ends of the DNA chains bearing 3'-hydroxyl groups 

 was further demonstrated by graded action of venom phosphodiesterase on 

 the products. In keeping with the mode of action of the latter enzyme as 

 recently elucidated, 59 the radioactivity residing in the added nucleotide (s) 

 was released in the time during which less than 3% of the total polymer 

 had been degraded. 



g. The Formation of Deoxyadenylic-Thymidylic Polymer 



A brief report has been made 90 of the highly interesting observation that 

 a copolymer of deoxyadenylic acid and thymidylic acid is formed by the 

 polymerase in the absence of any primer after a lag period of 3-6 hours. 

 This synthetic material can, in turn, serve as primer and thus abolish the 

 time lag in the synthesis of more of the same type of material. Even though 

 all the four deoxynucleoside-5'-triphosphates may be present, polymeriza- 

 tion occurs so as to form only the deoxyadenylic-thymidylic polymer. 



h. DNA Synthesis in T2 Phage-Infected Cells 



It is known that a phage-infected E. coli cell ceases to produce its own 

 DNA but makes instead the DNA characteristic of the infecting phage. 95 



92 J. Adler, I. R. Lehman, M. J. Bessman, E. S. Simms, and A. Romberg, Proc. Natl. 

 Acad. Set. U. S. 44, 641 (1958). 



93 L. Cunningham, B. W. Catlin, and M. P. deGarilhe, J. Am. Chem. Soc. 78, 4642 

 (1956). 



94 L. A. Heppel and R. J. Hilmoe, in "Methods in Enzymology" (S. P. Colowick and 

 N. O. Kaplan, eds.), Vol. II, p. 547. 



95 A. D. Hershey, J. Dixon, and M. Chase, J. Gen. Phi/si,,!. 36, 777 (1952-1953). 



