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RNA Processing:- Polynucleotide Phosphorylase Makes Random RNA-like Polymers

المؤلف:  David L. Nelson، Michael M. Cox

المصدر:  Lehninger Principles of Biochemistry

الجزء والصفحة:  1020

2026-07-25

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RNA Processing:- Polynucleotide Phosphorylase Makes Random RNA-like Polymers

In 1955, Marianne Grunberg-Manago and Severo Ochoa discovered the bacterial enzyme polynucleotide phos phorylase, which in vitro catalyzes the reaction

Polynucleotide phosphorylase was the first nucleic acid synthesizing enzyme discovered (Arthur Kornberg’s discovery of DNA polymerase followed soon thereafter).

The reaction catalyzed by polynucleotide phosphorylase differs fundamentally from the polymerase activities dis cussed so far in that it is not template-dependent. The enzyme uses the 5-diphosphates of ribonucleosides as substrates and cannot act on the homologous 5-triphosphates or on deoxyribonucleoside 5-diphosphates. The RNA polymer formed by polynucleotide phosphorylase contains the usual 3,5-phosphodiester linkages, which can be hydrolyzed by ribonuclease. The reaction is read ily reversible and can be pushed in the direction of breakdown of the polyribonucleotide by increasing the phosphate concentration. The probable function of this enzyme in the cell is the degradation of mRNAs to nucleoside diphosphates.

Because the polynucleotide phosphorylase reaction does not use a template, the polymer it forms does not have a specific base sequence. The reaction proceeds equally well with any or all of the four nucleoside diphosphates, and the base composition of the resulting poly mer reflects nothing more than the relative concentrations of the 5-diphosphate substrates in the medium. Polynucleotide phosphorylase can be used in the laboratory to prepare RNA polymers with many differ ent base sequences and frequencies. Synthetic RNA polymers of this sort were critical for deducing the ge netic code for the amino acids .