I. REPLICATION OF DNA IN CELL-FREE SYSTEMS 59 



that T4 DNA contains 707o o- and 307^ /?-gliico.syl linkages. Second, we 

 would expect that natural T4 DNA which has had some a-glucosyl 

 residues removed with the a-transferase and UDP (running the reaction 

 in reverse) should accept only a-glucosyl units, and similarly /3-degluco- 

 sylated DNA should accept only |8-glucosyl units. The data in Table 

 XXX, however, show that no matter which of the enzymes is used to 



TABLE XXX 



Addition of Glucose to "De-Glucosylated" T4 DNA" 



" From Josse and Kornberg (1962). 



remove the glucose units, both enzymes can put the glucose back in. 

 This would indicate that the sequence around the glucosyl units does not 

 direct the synthesis. Third, a polymer containing only dGMP and H]\IC 

 nucleotides was synthesized using d-GC polymer as primer. This new 

 polymer presumably had the structure d-GH]\lC with all the guanine 

 residues in one strand and all the H]\IC residues in the other. When 

 this polymer was used as an acceptor for glucosylation, all four of the 

 specific monoglucosyl transferases were active. This would mean that all 

 the enzymes were capable of glucosylating an HMC-residue bounded 

 on both sides by another HMC residue. 



If base sequence is not the determinant for insertion of glucose 

 residues, where else may we look? Josse and Kornberg (1962) point out 

 that the secondaiy or tertiary structure of the macromolecule may be 

 pertinent here. They indicate the heat-denatured DNA is markedly 

 altered in respect to rate of glucosylation and in some instances extent 

 of glucosylation. Indeed, the decrease in rate of glucosylation is so well 

 correlated with the "melting" of DNA that Zimmerman et al. (1962) 

 suggest the possibility of using the rate of glucosylation as a rapid, 

 sensitive index for measuring heat denaturation of DNA. 



At present, the mechanism which directs the positioning of glucosyl 

 units throughout the DNA molecule is unknown. Equally mysterious is 

 the function of glucose in bacteriophage DNA. 



