[Effect of various factors on the methylation of DNAse I]

The effects of NaCl, EDTA and tRNA on methylation and enzymatic properties of deoxyribonuclease I (DNase I) were investigated. The methylation was carried out by S-methylmethionine (vitamin U) in the phosphate-citric buffer pH 4.0. It was found that 0.5 M NaCl decreases by about 30% the incorporation of CH3-groups into the DNase, whereas 1.5 M NaCl-by 47%. A similar, although a less pronounced effect, was exerted by tRNA within the concentration range of 1.36-34.7 microM. On the contrast, EDTA (0.01-0.05 M) stimulated the incorporation of CH3-groups by 15 and 30%, respectively. The functional properties of methylated DNase I in the presence of EDTA remained unaffected. The enzyme methylation in the presence of NaCl or tRNA caused deceleration of the 3H-DNA hydrolysis (by 15-30%) only within the first 20 min of the reaction.