Favored incorporation of tubercidin in poly(adenylic, 7-deazaadenylic acids) and their function as messenger ribonucleic acids in protein synthesis

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Abstract
The following polynucleotides containing the antibiotic tubercidin (Tu; 4-amino-7-.beta.-D-ribofuranosylpyrrolo[2,3-d]pyrimidine) were enzymatically synthesized by polymerization of ADP tubercidin 5''-diphosphate mixtures with polynucleotide phosphorylase: poly(A2, Tu), poly(A,Tu2) and poly(Tu). The incorporation of the antibiotic was favored by the enzyme. The polymers are compared to poly(A) with respect to structure, conformation and ability to direct polylysine synthesis in an Escherichia coli ribosome-dependent protein synthesis system. From physical data (thermal melting, NMR and circular dichroism) it is concluded that tubercidin destabilizes the structure of the polynucleotide chain and this may be due to an altered polarization of the nucleobases and their enhanced rotation around the N-glycosylic bond. Since there is an apparent correlation between thermal unfolding of the polymers and their ability to mediate polylysine synthesis, it is suggested that partial destacking of the mRNA favors its binding to the ribosome and/or its ability to enhance codon-anticodon-specific protein synthesis.

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