Carbethoxylation of Polynucleotides

Diethyl pyrocarbonate has been shown to react with poly(A), poly(C) and poly(G) but poly(U) does not react. Diethyl pyrocarbonate appears to carbethoxylate amino groups on the bases. Poly(A) can bind one carbethoxy group per base but the binding capacity of poly(G) and poly(C) under non‐denaturing conditions is 0.32 and 0.23, respectively. The difference in binding between poly(A) on one hand and poly(G) and poly(C) on the other may depend on conformation of the polynucleotides. The double helix poly(A) · poly(U) is essentially not carbethoxylated and native adenovirus DNA does neither bind carbethoxy groups. Carbethoxylation of poliovirus RNA leading to a 3‐fold decrease in infectivity resulted in an average of 11 carbethoxy groups per RNA molecule. The specificity of the carbethoxylation for single strands was used to estimate the helix content of transfer RNA. Denatured yeast tRNA Ala was carbethoxylated on 55 out of 56 bases containing amino groups. 18 carbethoxy groups could be introduced under native conditions in the absence of magnesium, compared with 16 carbethoxy groups in the presence of magnesium. This is in agreement with the number of A, G and C in single‐stranded regions of the clover‐leaf model. Unfractionated yeast tRNA was carbethoxylated on 29 and 20 bases respectively in the absence and presence of magnesium. The results suggest that carbethoxylation could be used to determine secondary structure of RNA.