The Structure ofB-DNA in Oriented Fibers

Abstract
Native, general sequence B-form DNA in uniaxially oriented fibers is a ten-fold helix with identical antiparallel strands: this is to say the molecular symmetry is 2 2 101. The diffraction patterns indicate that local variations, however significant, must be modest. This is true also for the lithium salt of calf thymus DNA in fibers that are polycrystalline as well as oriented. The contents of its orthorhombic unit cells are arranged with P212121 symmetry which permits the molecular symmetry to be merely two-fold. The molecular structure of DNA in such conditions resembles, conformationally and molecularly, that of B-type DNA in oligonucleotide single crystals and in oriented polycrystalline fibers of polyoligonucleotides, and therefore provides a basis for evaluating the variations that may be due to sequence effects in polyoligonucleotides in fibers and oligonucleotides in single crystals.

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