A lipopolysaccharide inhibitor of a DNA methyl transferase.

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Abstract
An inhibitor of a purified deoxyribonucleic-acid (DNA) methyl transferase has been identified in culture media of E. coli producing M 13 phage. Although associated with the phage, the inhibitor was separated from it by CsCl gradient centrifugation and was identified with the cell wall lipopolysaccharide of gram -negative bacteria. Extracts of E. coli contain a factor which neutralized the activity of the inhibitor. This DNA methyl transferase, induced by T2 infection, and relatively specific for adenine residues, does not transfer to synthetic DNA-like polymers which among them contain all seven possible dinucleotide sequences with adenine; in addition, seven of the possible 37 triplets with adenine have been excluded as acceptors. The enzyme does not distinguish in the extent of methyla-tion (0.4% of the total base residues) between calf thymus DNA and DNA from B. subtilis spores or vegetative cells.