Polynucleotide phosphorylase functions both as a 3′ → 5′ exonuclease and a poly(A) polymerase in Escherichia coli

Polynucleotide phosphorylase functions both as a 3′ → 5′ exonuclease and a poly(A) polymerase in Escherichia coli

Bijoy K. Mohanty and
Sidney R. Kushner*

Department of Genetics, University of Georgia, Athens, GA 30602-7223

Edited by Sidney Altman, Yale University, New Haven, CT, and approved August 18, 2000 (received for review June 27, 2000)

Abstract

In vitro, polynucleotide phosphorylase of Escherichia coli can both synthesize RNA by using nucleotide diphosphates as precursors and exonucleolytically degrade RNA in the presence of inorganic phosphate. However, because of the high in vivo concentration of inorganic phosphate in exponentially growing cells, it has been assumed that the enzyme works exclusively as an exonuclease. Here we demonstrate that, contrary to this prediction, polynucleotide phosphorylase not only synthesizes long, highly heteropolymeric tails in vivo, but also accounts for all of the observed residual polyadenylylation in poly(A) polymerase I deficient strains. In addition, the enzyme is responsible for adding the C and U residues that are found in poly(A) tails in exponentially growing cultures of wild type E. coli.

Footnotes

↵ * To whom reprint requests should be addressed. E-mail: skushner{at}arches.uga.edu.
This paper was submitted directly (Track II) to the PNAS office.
Article published online before print: Proc. Natl. Acad. Sci. USA, 10.1073/pnas.220295997.
Article and publication date are at www.pnas.org/cgi/doi/10.1073/pnas.220295997
Abbreviations:

PNPase,

polynucleotide phosphorylase;

PAP,

poly(A) polymerase