P-B1-41 Stereochemistry and structures of 2′,5′ linked DNA and RNA duplexes and trnplexes. A generalised concept of compact and extenoed nucleotide to unify helix generation in 2′,5′ and 3′,5′ nucleic acids: Yathindra N, Lalitha, V, Department of Crystallography & Biophysics, Univ. of Madras, Madras, India 600 025