[Sensitivity of B- and C-DNA forms to modifications by O-methylhydroxylamine]

Effects of high concentrations of lithium, cesium and ammonium chlorides on the reaction ability of free CMP and cytosine in free DNA of CD phage with respect to O-methylhydroxylamine (OMHA) are studied. CMP reaction in all the cases takes place mainly for 24 hours. Like classical B-form, native DNA, having C-form in high ionic strength solution (as estimated from circular dichroism data), is not modificated. Thus, the access of some cytosine residues in intraphage DNA to OMHA is due not to the decreased DNA hydratation in situ, but to the presence of differently ordered regions in DNA.