Deoxyribonucleic acid modification methylase from Bacillus stearothermophilus

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Abstract
A modification methylase was isolated from B. stearothermophilus 1503-4R (Bst1503I) and purified to homogeneity. The enzyme is an acidic protein and composed of a subunit with a MW of 105,000 and only the tetrameric form was detected in solution. The methylase exhibited maximal activity 54.degree.-61.degree. C and between pH 8.1-9.3. In contrast to Bst1503I endonuclease, the methylase is completely inactivated when exposed to temperatures near the optimal growth temperature (63.degree.-67.degree. C). The methylase was also inactivated when exposed to temperatures below the minimal growth temperature (48.degree.-53.degree. C). The thermostability of the methylase is significantly enhanced by Na+, K+ or NH4+. Membrane-bound methylase is resistant to heat inactivation at temperatures near the maximum growth temperature (73.degree.-75.degree. C). The methylase functions as a tetramer. The initial rates of methyl transfer are first order in methylase concentration and the enzyme obeys Michaelis-Menten kinetics with respect to DNA but not to S-adenosyl-L-methionine.

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