Sequence-Dependent Liquid Crystalline Ordering of Gapped DNA.

We investigate the impact of poly adenine (poly-A) sequences on the type and stability of liquid crystalline (LC) phases formed by concentrated solutions of gapped DNA (two duplex arms bridged by a flexible single strand) using synchrotron small-angle X-ray scattering and polarizing optical microscopy. While samples with mixed sequence form layered (smectic) phases, poly-A samples demonstrate a columnar phase at lower temperatures (5-35 °C), not previously observed in GDNA samples, and a smectic-B phase of exceptional stability at higher temperatures (35-65 °C). We present a model that connects the formation of these LC phases with the unique characteristics of poly-A sequences, which manifest in various biological contexts, including DNA condensation and nucleosome formation.