DNA double helical fragment at atomic resolution

Abstract

Details of the molecular architecture of double helical ribonucleic acids at atomic resolution have recently become available from single crystal X-ray diffraction studies of dinucleotides composed of complementary bases. No similar studies have been published for deoxynucleotides. We report here the structure of the deoxytetranucleotide d-pApTpApT (5′-P-adenylyl-(3′-5′)-thymidylyl-(3′-5′)-adenylyl-(3′-5′)-thymidine) (I) at a resolution of 1.0 Å. This is the first tetranucleotide whose structure has been elucidated by X-ray diffraction. The work is part of an investigation of protein–nucleic acid interactions using single-crystal studies of small model compounds. d-pApTpApT was chosen as one of the first compounds to be examined because there is evidence that poly(dA–dT) has unusual binding properties and that A.T-rich regions in certain DNAs have specific biological roles. We hope that these investigations will provide information about the influence of specific base pairs and sequences on the fine details of the DNA structures, and thus aid the understanding of the selective recognition of nucleotide sequences of the DNA double helix by proteins.