CHEMICAL MODIFICATION OF VIRAL RIBONUCLEIC ACID .7. ACTION OF METHYLATING AGENTS AND NITROSOGUANIDINE ON POLYNUCLEOTIDES INCLUDING TOBACCO MOSAIC VIRUS RIBONUCLEIC ACID

N-MethvI-N′-nitro-N-nitrosoguanidine methylates the same positions on the guanine, adenine, and cytosine residues as typical alkylating agents, although at a much slower rate. Guanine and adenine react more readily with nitrosoguanidine under conditions favoring base stacking (polymers in aqueous solution), and the opposite is true for cytosine. The action of typical methylating agents is not affected by this conformation. The depressed reactivity of the 1 and 3 positions of complementary base-paired adenine and cytosine, respectively, toward dimethyl sulfate has been con- firmed, and observed to be true also for nitrosoguanidine, as far as adenine is concerned (cytosine being poorly reactive in aqueous solutions). Methylation by both types of reagents gives relatively more 7-methyladenine and 3-methyladenine than generally reported, and these reactivities remain unaffected when the formation of 1-methyladenine is depressed by base pairing. Treatment of ribonucleic acid with nitrosoguanidine does not produce detectable levels of nitrosation, but some deamination occurs upon prolonged treatment with the reagent. © 1969, American Chemical Society. All rights reserved.