Antibodies recognise specific structures of triple-helical polynucleotides built on poly(A) or poly(dA)

Abstract

ANTIGENIC determinants of nucleic acids may comprise individual bases or base sequences, as in denatured DNA, or specific conformational features, as in helical forms1. Experimentally induced antibodies have shown selective reactivity toward double-stranded RNA2–6, RNA–DNA hybrids4, or distinct features of poly(G) · poly(C)7 or poly (dG) · poly(dC)4. Some of these antibodies can be used to identify double-helical RNA in virus-infected cells8,9 and to quantitate it in RNA extracted from such cells10, or to distinguish between double-stranded RNA and RNA–DNA hybrids in mixtures of enzyme reaction products11. Triple-helical poly(A) · 2poly(U) can also be distinguished from double-helical forms2,9. Triple-helical regions can form where continuous purine sequences occur12, and they might be involved as intermediates or as recognition sites in transcription13,14. Thus antibodies that recognise triple-helical nucleic acids are important in the definition of conformation-dependent antigenic determinants, as a model for protein recognition of specific nucleic acid sites, and they may identify such sites in naturally occurring nucleic acids. We describe here such antibodies that can differentiate three-stranded structures built on poly(A) from others built on poly(dA).