Synthesis and coding properties of poly(c 1A), poly(c 3A), poly(c 7A) and poly(h 6A)

Abstract

The homopolynucleotides poly(c 1A), poly(c 3A), poly(c 7A) and poly(h 6A) ++ ++ These compounds are symbolized, according to the recommendations of the IUPAC-IUB Commission on Biochemical Nomenclature (Europ. J. Biochem. 15 (1970) 203) as follows: c 1Ado = 1-deazaadenosine, c 3Ado = 3-deazaadenosine, c 7Ado = 7-deazaadenosine = tubercidine, h 6Ado = purineriboside = nebularin (see Fig. 1). were synthesized from their corresponding nucleoside diphosphates using polynucleotide phosphorylase. With the exception of poly(h 6A), which displayed no hypochromicity, the homopolynucleotides showed melting profiles similar to poly(A). All these polynucleotides, poly(h 6A), poly(c 7A), poly(c 3A) and poly(c 1A) stimulated the binding of Lys-tRNA to ribosomes; the coding activity of poly(c 1A), however, was very low. Poly(h 6A) was found to be less specific for Lys-tRNA than poly(A). The data supports the exclusive formation of Watson-Crick type base pairs and contradicts Hoogsteen base pairing in codon-anticodon recognition. Since, however, poly(h 6A), which can form only one hydrogen bridge per base pair, stimulated the binding of Lys-tRNA comparably to poly(A), the coding activity of the homopolynucleotides tested is discussed in respect to their secondary structure as well as to the pK-values of their 6-amino groups.