Although, I didn't believe it when I first saw it. With all the years that I've heard (or taught) that all DNA is antiparallel, it was hard to believe my eyes.
Yet here is parallel DNA, with both strands oriented in the same direction, right here on your monitor. And the commenters were correct.
The image that I posted a couple of days ago was made from part of this same structure. In that image, I hid the rest of the bases to make it easier to see why this structure is so strange.
Here are two images that show the landmarks a bit better. I hid the hydrogens and used different rendering styles to emphasize key features in the sugar phosphate backbone.
Part of the mystery is what the people who deposited this structure were trying to do in the first place and why they synthesized this molecule. Unfortunately, the article that's referenced in the database is in a journal that's not indexed by PubMed or Google and there isn't a PubMed Central reference.
We're left to wonder.
But if you want to find out, and you have access to a good library, the reference is below.
Venkitakrishnan,R.P. et. al. 2004. A Parallel Stranded Dna Duplex With An A-G Mismatch Base-Pair:
(Ccataatttacc:cctatgaaatcc). Recent Trends In Biophys.Res., 1