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directly.

GENERAL INFORMATION

1. Title of website:
	Worldwide Protein Data Bank

2. Contributor information:
	Moore, M.H. (University of York)
	Van Meervelt, L. (Katholieke Universiteit Leuven [KU Leuven])
	Salisbury, S.A. (Cambridge Crystallographic Data Centre)
	Kong Thoo Lin, P. (Robert Gordon University)
	Brown, D.M. (MRC Laboratory of Melecular Biology)
	
3. Date on which website first launched:
	1995-12-09
	
4. Funding:
	National Fund for Scientific Research (Belgium)
	Research Council of the K.U. Leuven (Belgium)
	Medical Research Council
	Engineering and Physical Research Council
	

ACCESS INFORMATION

1. Access Links:
	https://doi.org/10.2210/pdb223d/pdb
	https://web.archive.org/web/20221027101038/https://www.wwpdb.org/pdb?id=pdb_0000223d (archived 
	2022-10-27)
	
2. Recommended citation:
	MOORE, M.H., VAN MEERVELT, L., SALISBURY, S.A., KONG THOO LIN, P. and BROWN, D.M. 1995. Direct 
	observation of two base-pairing modes of a cytosine-thymine analogue with guanine in a DNA 
	z-form duplex: significance for base analogue mutagenesis. [Dataset]. Hosted on Worldwide 
	Protein Data Bank (wwPDB) [online], 223D. Available from: https://doi.org/10.2210/pdb223d/pdb
	
	
CONTEXTUAL INFORMATION

1. Abstract:
	The pyrimidine nucleobase analogue 6H,8H-3,4-dihydropyrimido[4,5-c]-[1,2]oxazin-7-one (P) is a 
	mimic both of cytosine and thymine, since it can form stable hydrogen-bonded base-pairs with 
	either guanine or adenine. To investigate the geometric properties of pairing with guanine in a 
	DNA double helix, the structure of d(CGCGPG)2 has been determined by single crystal X-ray analysis. 
	The oligonucleotide crystallised as a left-handed Z-DNA duplex in the orthorhombic space group 
	P212121 with cell dimensions a = 18.23 Å, b = 30.63 Å, c = 43.78 Å. Refinement using NUCLSQ with 
	51 water molecules included in the final model converged at R = 0.179 (Rw = 0.159) for 2798 
	reflections (F > 2s(F)) in the range 8 Å to 1.7 Å. Remarkably, the two P·G pairs in the hexamer 
	duplex are different: UK Watson-Crick and wobble types separately illustrate both cytosine-like 
	and thymine-like behaviour. The result suggests that mutagenesis experiments involving P and other 
	analogues which display pronounced base-pairing ambivalence can be used to examine the structural 
	basis of substrate discrimination by polymerases that is essential to accurate genetic replication. 
	The data for this output can be found at https://doi.org/10.2210/pdb223d/pdb.