1. N4-substituted cytosine derivatives are formed in good yield in aqueous solutions containing bisulfite ions and cytosine, cytidine or cytidine 5'-phosphate, on the one hand, and glycine, glycyl-glycine, or poly-L-lysine, on the other hand. The products are models of the cross-links arising within nucleoproteins on treatment with nucleophilic reagents, and, probably, those arising after photohydratation of cytosine residues.2. The effects of temperature, reagent concentrations, and pH on the reaction kinetics were studied. The maximum rate of transamination and minimum deamination are observed at pH 7.2-7.4. Changes of temperature between 6 and 25°C do not affect the ratio of the rates of the two reactions.3. The compounds obtained are stable under conditions of alkaline and acidic degradation of polyribonucleotides. Complete cleavage of the N-glycosidic bonds with 6 N HCl (110°C, 96 hr) or 70% HC1O4 (100°C, 1 hr) is accompanied by less than 10-20% cleavage of the bond between the pyrimidine nucleus C4-position and the amino acid residue amino group.4. With the polylysine derivative of cytidine, it was demonstrated that the N-C4bond can be cleaved by nucleophilic reagents such as O-methylhydroxylamine and bisulfite-O-methylhydroxylamine mixture. © 1973 BY THE JOURNAL OF BIOCHEMISTRY.