Mohanty B K, Kushner S R
Department of Genetics, University of Georgia, Athens, GA 30602-7223, USA.
Proc Natl Acad Sci U S A. 2000 Oct 24;97(22):11966-71. doi: 10.1073/pnas.220295997.
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.
在体外，大肠杆菌的多核苷酸磷酸化酶既能以二磷酸核苷酸为前体合成RNA，又能在无机磷酸盐存在的情况下进行核酸外切降解RNA。然而，由于指数生长期细胞内无机磷酸盐的浓度很高，人们一直认为该酶仅作为核酸外切酶起作用。在这里，我们证明，与这一预测相反，多核苷酸磷酸化酶不仅在体内合成了长的、高度异聚的尾巴，而且解释了在缺乏聚腺苷酸聚合酶I的菌株中所有观察到的残留聚腺苷酸化现象。此外，该酶负责在野生型大肠杆菌指数生长期培养物的聚腺苷酸尾巴中添加C和U残基。
