A new reaction useful for chemical cross-linking between nucleic acids and proteins.

Cytosine in nucleic acids can be converted into N4-aminocytosine by treatment with a mixture of hydrazine and bisulfite. The hydrazino group thus formed at position 4 of the pyrimidine ring can be linked to a sulhydryl group in proteins by the use of bromopyruvate as a linker. Successful use of this scheme of chemical cross-linking between nucleic acid and protein was demonstrated in the linking of poly(C) with glutathione, and of RNA with protein in the E. coli 30 S ribosomal subunit.