Principles of Biochemistry Volume 3 - A. Lehninger 1985

Molecular Mechanisms of Genetic Information Transfer
DNA Replication and Transcription
Polynucleotide phosphorylase enables the synthesis of RNA-like polymers with a non-specific nucleotide sequence

In 1955, Marianne Grunberg-Manago and Severo Ochoa discovered polynucleotide phosphorylase, the first enzyme found capable of synthesizing long polynucleotide chains. (Shortly thereafter, Arthur Kornberg reported the Discovery of DNA polymerase.) Polynucleotide phosphorylase, which appears to be found exclusively in Bacteria, catalyzes the reaction

Class="center">NDP + (NMP)n⇄ (NMP)n+1 + Рi

where NDP is a nucleoside-5'-diphosphate, (NMP)n+1 is an extended polynucleotide, and Рi is the released phosphate. The enzyme requires ribonucleoside 5'-diphosphates; it cannot utilize ribonucleoside 5'-triphosphates, deoxyribonucleoside 5'-diphosphates, nor can it function in the absence of Mg2+ ions. Polynucleotide Phosphorylase catalyzes the synthesis of an RNA-like polymer containing 3',5'-phosphodiester bonds, which are hydrolyzed by Ribonuclease. The Hydrolysis reaction is readily reversible and can be driven toward polyribonucleotide Cleavage by increasing the phosphate concentration.

Polynucleotide phosphorylase is template-independent and does not synthesize polymers with a specific nucleotide sequence. It merely requires an RNA chain as a primer simply to provide a free 3'-hydroxyl terminus to which additional residues can be attached. The reaction proceeds both in the presence of all four starting monomers and in the presence of just a single one. The Nucleotide Composition of the resulting polymer reflects the relative Proportions of the precursor 5'-diphosphates in the medium. Therefore, it is unlikely that polynucleotide phosphorylase Functions in RNA Biosynthesis under natural conditions; rather, it is likely involved in RNA degradation.

Polynucleotide phosphorylase is a highly valuable research tool because it can be used in the laboratory to produce numerous RNA-like polymers with diverse nucleotide sequences and varying base compositions. As we will see later (Chapter 29), such synthetic RNA polymers made it possible to decipher the dictionary of amino acid code "words".



Last update: 06/08/2026

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