58 



MAURICE J. BESSMAN 



TABLE XXIX 

 Comparison of the Mo\o(;hcosyl Traxsferase" 



" From Josse and Kornberg (1962). 



^ In phosphate buffer. 



■^ In Ammediol l)uffer (2-amino, 2-methyl, 1,3-propanedioI). 



A study of the reversibility of the reaction with the T2 a-transferase 

 (Zimmerman et al., 1962) indicates that glucosyl residue.^ may be 

 removed from glucosylated Hj\IC DNA in the presence of UDP but the 

 equilibrium strongly favors the forward reaction: 



A' = 



(glucos yl-HMC)(UDP) 

 (HMC)(rDP-glucose) 



200 2000 



Thus, the extent of glucosylation is probably not limited by equilib- 

 rium considerations since 25% of the available sites in T2 DNA are 

 unglucosylated, and incubation in the presence of T2 a-transferase and 

 UDP-glucose does not further glucosylate it. 



What then does control the number and positioning of the glucosyl 

 residues in the different DNA types? The simplest hypothesis is that 

 specific base sequences determine the addition of glucosyl units. Recent 

 experiments by Josse and Kornberg (1962) do not tend to support this 

 notion although they do not exclude it. First of all, as had already been 

 observed by Kornberg et al. (1961), T4 ^-glucosyl transferase can 

 glucosylate 100% of the available HMC residues in DNA. We know 



