5-Methylcytosine content in the vertebrate deoxyribonucleic acids: species specificity.

RNA-free native DNA samples, isolated by four methods, from different vertebrate tissues and species, were hydrolyzed chemically and enzymatically and analyzed by paper chromatography to estimate the base composition. It was noted that (i) all the DNA preparations analyzed contained 5-methylcytosine, (ii) on the basis of mole percent of 5-methylcytosine, the composition of DNA varied in different species, but not so much in different tissues of the same species, (iii) the method of DNA hydrolysis, but not the method of deproteinization, affected the mole percent of 5-methylcytosine, and (iv) no 5-hydroxymethylcytosine (5-HMC) was detected in any of the DNA preparations analyzed.