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BIOCHEMISTRY: KORNBERG ET AL. 



Proc. N. a. S. 



were used, no glucose fixation in DNA was detectable (Table 1). dHMC-5-P 

 and dHMC-TP failed to substitute for HMC-containing DNA as glucose acceptors. 

 For example, in an incubation mixture containing these three types of HMC com- 

 pounds with 30-fold purified enzyme, the HMC-DNA fixed 46 per cent of the glucose 

 of the UDPG, while dHMC-5-P and dHMC-TP fixed none «0.5 per cent). 



10 20 30 



TIME - minutes 



Fig. 4. — DNA-glucosylating enzyme levels before and after 

 infection with phage T2 or T5. The arrow indicates the start of 

 infection ("zero minutes," see Method I). The incubation mix- 

 tures (0.20 ml) contained: 10 mjumoles of UDPG labeled uni- 

 formly with Ci'' in the glucose residue (2 X 10^ cpm per mMmole), 

 Tris buffer, pH 7.5 (0.1 M), glutathione (0.02 M), DNA synthe- 

 sized enzymatically (using thymus or phage T2 DNA as primer) 

 and containing about 1 mjumole of HMC, and extract containing 

 10-50 ixg of protein. After 15 min of incubation at 30°, the mix- 

 ture was treated as in the "polymerase" assay of incorporation 

 of a labeled deoxynucleotide into an acid-insoluble product (see 

 Methods). 



In the presence of an excess of HMC-DNA, the glucose of UDPG is transferred 

 completely to the DNA. With an excess of UDPG and enzyme, the fixation of 

 glucose in DNA reaches a limiting value, which is a function of the HMC-DNA 

 present (Fig. 5). The number of glucose residues fixed in this experiment was 

 approximately 60 per cent of the number of HMC residues in the added DNA. 

 At this point it may be premature to regard the glucosylation limit observed with 



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