PREOPENED STATE OF DNA DUPLEX

A theoretical study was made of the formation of a metastable DNA stat e characterized by accessibility of the nucleic base amino groups for modifying agents. It was assumed that base pair preopening is preceded by base tautomerization and conformational changes in the duplex. The model proposed for the preopened base pair allows one to explain the mechanism of interaction of the base amino groups with formaldehyde an d exchange of amino protons. The probability of base pair preopening w as shown to be 10(-3)-10(-2). This value is consistent with the experi mental data.