Analysis of products of DNA modification by methylases: a procedure for the determination of 5- and N4-methylcytosines in DNA.

Although many different methods are used for the identification of methylated heterocyclic bases in DNA not all of them possess the ability to discriminate N4-methylcytosine (m4C) and 5-methylcytosine (m5C). Therefore, some of the methods need additional reexamination. This paper reinvestigates some chromatographic systems (thin-layer chromatography, paper chromatography, electrophoresis) most widely used in the analysis of minor bases occurring in nucleic acids according to their ability to separate m4C and m5C. A simple procedure for the preparation of the sample and a chromatographic system for its analysis was developed. The recommended chromatographic systems may be used for the simultaneous separation of not only of m4C and m5C but also both methylated cytosines together with N6-methyladenine and 7-methylguanine.