The accessibility of 5-methylcytosine to specific antibodies in double-stranded DNA of Xanthomonas phage XP12

Abstract

Antibodies specifically directed to 5‐methylcytidine were raised in rabbits and purified by affinity chromatography. The accessibility of 5‐methyldeoxycytidine (m⁵dCyd) to such antibodies was studied with DNAs from various origins. The reaction was followed by measuring the retention of radiolabelled DNA by antibodies on nitrocellulose filters, by immunoprecipitation, by gel filtration and was visualized with the electron microscope. Antibodies did not bind to Escherichia coli B DNA, which is deficient in m⁵dCyd. Denatured and native DNA from calf thymus, which contains m⁵dCyd as a minor nucleoside, was weakly retained on the filters whereas DNA extracted from Xanthomonas oryzae XP12 bacteriophage, which is rich in m⁵dCyd, was well recognized even in the native form.