Intramolecular i-motif structure at acidic pH for Progressive Myoclonus Epilepsy (EPM1) repeat d(CCCCGCCCCGCG)(n)

The most common mutation associated with Progressive Myoclonus Epilepsy (EP M1) of Unverricht-Lundberg type is the expansion of a dodecamer repeat, d(C CCCGCCCCGCG)n. We show that the C-rich strand of this repeat (2-3 copies) f orms intercalated i-motif structure at acidic pH as judged by CD spectrosco py and anomalous gel electrophoretic mobility. The stability of the structu re increases with the increase in the length of the repeat. Transient forma tion of stable, folded back structure like i-motif could play an important role in the mechanism of expansion of this repeat.