| Abstract
| - The deoxyoligonucleotide d(Br U-G-C-G-C-G) was crystallised at pH 8.2 and its structure analysed by X-ray diffraction. The unit cell, of dimensions a=17.94, b=30.85, c=49.94°A contains four DNA duplexes in space group P2l2l2l . The duplexes are in the Z conformation, with four Watson-crick G.C base pairs and two BrU.G base pairs. The structure was refined to an R factor of 0.16 at a resolution of 2.2°A with 64 solvent molecules located. The BrU.G base pair mismatch is of the wobble type, with both bases in the major tautomer fornuand hydrogen bonds linking 0-2 of BrU with N-l of G and N3 of BrU with 0-6 of G. There is no indication of the presence of ionised base pairs, in spite of the high pH of crystallisation. The results are discussed in terms of the mutagenic properties of 5- bromouracil.
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