The Preparation of Nucleotide-Protein Conjugates: Carbodiimides as Coupling Agents

Abstract

For some time it has been apparent that antibodies might be useful in the study of the fine structure of RNA and DNA. A major stumbling block has been the unavailability of a method which would render polynucleotides antigenic yet largely preserve their structural integrity. In approaching the problem of covalently conjugating polynucleotides to proteins as a means of stimulating antibody formation, we sought a procedure which would employ terminal nucleotide PO₄ or OH groups for coupling. Two ways in which the terminal PO₄ groups might be coupled covalently to protein would involve formation of a phosphodiester bond with protein seryl and threonyl residues or an N-P bond with protein ε-amino groups (Fig. 1, reactions 1 and 2 respectively). On the other hand, the OH group of a terminal sugar residue could react with protein carboxyl groups forming an ester (Fig. 1, reaction 3).