Figure 1.
DNA structures formed by simple DNA repeats. A: H-DNA formed by GAA/TTC sequences. As shown, the homopurine (GAA) strand is donated to the triplex. Dots indicate Watson-Crick base pairing. Asterisks indicate reverse Hoogsteen base pairing. B: Imperfect hairpin formed by (CNG)n repeats. C: G-quadruplex formed by (CGG)n repeats. Grey squares represent hoogsteen basepairing between four guanines. D: The G-rich strand of telomeres can form G guadruplex structures. One possible example is shown here. The T-loop results from invasion of the single-stranded telomeric 3′-overhangs into the upstream telomeric duplex DNA.