Assays for studying DNA methylation
Plant DNA is known to contain 5-methylcytosine as the only modified base. The methylation of plant DNA has been shown to take place exclusively at CpG and CpXpG sequences . In mammalian systems  and in bacteria  the enzymatic reaction of DNA methylation has been found to be a post-replicative process carried out by a maintenance type methyl transferase operating by a semiconservative mechanism . Surprisingly there is, as yet, no report describing the isolation and characterization of a plant DNA methyl transferase. However, it is believed that the principal characteristics of plant DNA methylases will turn out to be similar to the known features of the mammalian enzymes that have so far been characterized and described [5–7]. Nevertheless, it should be kept in mind that the sequence specificity of the plant DNA methylation is not identical to that of other eukaryotic systems. While the mammalian methylase modifies exclusively CpG sequences, the plant methylase must recognize and methylate CpXpG as well . Based on the well established fact that the methylated sites are symmetrically methylated on both strands [1, 8, 9], the mechanism of DNA methylation in vivo can be predicted. It has been suggested that during replication the maintenance methyl transferase activity faithfully copies the methylation pattern of the parental DNA strand to the newly replicating strand .
KeywordsNitrocellulose Filter Restriction Enzyme Analysis Micrococcal Nuclease CCGG Site Bunsen Flame
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