We have reported that production and characterization of antibodies highly specific to 5-methyl-cytosine (SmC) and the development of a sensitive immunochemicai method for the detection of 5mC in DNA [EBBS Lett. (1982) 150, 4691. Extension of this method to two other modified bases, 6-m~hyladenine (6mA) and %methyiguanine (7mG), is reported here. By use of this immunochemical approach, we are able to detect 5mC, 6mA and 7mG in human and Drosophila DNA and confirm their presence in the DNA of two mealybug species. DNA methylation Biotin-avidin cross-linking DNA-protein interaction Z-DNA X-chromosome inactivationGene regulation

We have previously reported a sensitive immunochemical method for detecting 5‐methylcytosine in DNA which involves spotting DNA samples on nitrocellulose paper and detection of 5‐methylcytosine, if any, by a combination of the double antibody method and a staining reaction brought about by biotin‐avidin and peroxidase. We report here a linear relationship between the concentration of 5‐methylcytosine in DNA and staining intensity, as recorded by photoacoustic spectroscopy. It appears possible to obtain, by this method, reliable quantitative estimates of 5‐methylcytosine in nanogram quantities of intact DNA. When Drosophila melanogaster DNA was assayed for the presence of 5‐methylcytosine by this method, a faint but clearly positive reaction was obtained. When the photoacoustic intensity of this stained spot is compared with a calibration plot derived from phi X174 DNA whose 5‐methylcytosine content is known, we obtain, for D. melanogaster DNA, one 5‐methylcytosine residue in approximately 12 500 bases or 0.008 mol% methylation.