CHARACTERIZATION OF THE STRUCTURAL CONFORMATION ADOPTED BY (TTAGGG)(N) TELOMERIC DNA REPEATS OF DIFFERENT LENGTH IN CLOSED CIRCULAR DNA

Telomeric DNA sequences are known to adopt unusual DNA structures upon protonation when contained into negatively supercoiled DNA. In this p aper, the structural properties of (T(2)AG(3))(n) telomeric sequences of different length is analyzed in detail. Transition to the protonate d form is observed at very low pH for (T(2)AG(3))(n>8) sequences. Form ation of the protonated form is facilitated by negative supercoiling. The patterns of chemical modification obtained with different chemical reagents indicate that protonation induces denaturation of the (T(2)A G(3))(n) telomeric sequences. Upon denaturation, the ''C-rich'' strand becomes structured forming, most likely, hairpin-like conformations s tabilized by the formation of C+ . C pairs and, probably, of A(+) . A pairs. The ''G-rich'' strand of the (T(2)AG(3))(8) sequence shows also signs of becoming structured giving rise to various structural confor mers which might include triple- and tetra-stranded conformations. How ever, in the case of shorter sequences, the ''G-rich'' strand remains basically single-stranded.