Method for the introduction of the reactive functional groups via cytidine residues and/or 3'-terminal of the nucleic acids.

: A number of polyfunctional O-substituted hydroxylamines H2NO-R-X (X = SH; -NH2; -P(O) (OH)2; -COOH; etc.) were constructed and synthesized as a mean for the administration of the reactive functions through cytidines or into 3 -oxidised terminal of nucleic acids.