POLYNUCLEOTIDES .12. FURTHER STUDIES ON POLY G.POLY C AND DNA

Physical parameters such as ultraviolet absorption, fluorescence and optical rotatory dispersion of poly G·poly C have been followed as a function of pH. The results indicate that before acid-induced strand separation occurs, a new secondary structure with a specific conformation is formed. Similar studies of the protonation of DNA and of DNA methylated at N7 of the guanine residues, indicate that this same modified conformation may arise in GC-rich regions (with a linear rather than alternating sequence of G or C residues, though random sequences are not excluded) of the DNA in the course of protonation. The results show that most of the cytosine residues are protonated before significant protonation of deoxyguanosine residues occurs. © 1969.