This report represents one of the earliest studies of base analogs, in order to affect the native base pairing of DNA and RNA molecules. Deoxyinosine is a base that can base pair with each of the 3 other bases (C, A and T). The method of optical melting was used to assess the thermal stability of DNA duplexes containing dI, when matched with each of the four DNA bases. The double strand molecules used in this study were obtained by combining equimolar amounts of a 9mer dCA3XA3G with the complimentary 9mer dCT3YT3G where X and Y were A, C, G, T, or I., respectively. Experimental results showed that A:T pairs were more stable than I:C pairs. Interestingly neighboring-base effects were noted, i.e.: when (X,Y)=(I,A), the double strand is about eight-fold more stable than when (X,Y)=(A,I).
Very helpful information was determined by establishing that the order of stabilities was found to be: I:C > I:A > I:T = I:G. This order of stability differs from that of dG which base pairs with dA with less strength; other than that each dI base pairs less stably than the corresponding dG counterpart, assuming the same sequence environment. It should be said that this work proved very useful in the design of probes for the isolation of the erythropoietin gene in 1983 and further stimulated probe design for the isolation of many other gene targets.
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