The X-ray crystal structure of a parallel poly(rA) double helix generated by rA7 at acidic pH
Crystal structure of a poly(rA) staggered zipper at acidic pH: evidence that adenine N1 protonation mediates parallel double helix formation.
rA7 dissolved in water to 10 mM and was diluted 1/10 v/v in 0.75% PEG 1000. One uL of this was mixed with 1 uL of the following reservoir solution: (0.24 M ammonium sulfate and 0.06 M citric acid pH 3.5) to generate a hanging drop over 1 mL of this reservoir solution.
National Institutes of Health/National Institute of General Medical Sciences (NIH/NIGMS)
National Institutes of Health/National Cancer Institute (NIH/NCI)
The asymmetric unit is rA2, however the input RNA polymer is rA7, and this forms a continual parallel poly(rA) double helix structure. This structure is referred to as a "staggered zipper" since the rA7 strands overlap in a many different registers relative to their opposite, paired strands, to form the helix.
parallel double-helix poly(rA) acidic pH adenine N1 protonation, RNA