Occurrence of 5-Methyl-Cytosine in Nucleic Acids

Abstract

THE presence in a nucleic acid of the pyrimidine 5-methyl-cytosine was first reported in 1925 by Johnson and Coghill¹, who claimed its discovery among the hydrolysis products of tuberculinic acid. As their identification, however, was based solely on the optical properties of the crystalline picrate, the correctness of this report has been subject to speculation; yet until the recent application of paper chromatography to nucleic acid analysis, there has been no published attempt to confirm their finding. Recently, using a chromatographic method, Vischer, Zamenhof and Chargaff² have estimated the purines and pyrimidines in deoxypentose nucleic acid from avian tubercle bacilli, and could find no trace of methyl-cytosine. Hotchkiss³, however, has noted in hydrolysed thymus nucleic acid a small amount of a substance the chromatographic behaviour and ultraviolet absorption spectrum of which are compatible with its being 5-methyl-cytosine.