Nuclear and chloroplast poly(A) polymerases from plants share a novel biochemical property

Poly(A) polymerases are centrally involved in the process of mRNA 3' end formation in eukaryotes. In animals and yeast, this enzyme works as part of a large multimeric complex to add polyadenylate tracts to the 3' ends of precursor RNAs in the nucleus. Plant nuclear enzymes remain largely uncharacterized. In this report, we describe an initial analysis of plant nuclear poly(A) polymerases (nPAPs). An enzyme purified from pea nuclear extracts possesses many features that are seen with the enzymes from yeast and mammals. However, the pea enzyme possesses the ability to polyadenylate RNAs that are associated with polynucleotide phosphorylase (PNP), a chloroplast-localized enzyme involved in RNA turnover. Similar behavior is not seen with the yeast poly(A) polymerase (PAP). A fusion protein consisting of glutathione-S-transferase and the active domain of an Arabidopsis-encoded nuclear poly(A) polymerase was also able to utilize PNP, indicating that the activity of the pea enzyme was due to an interaction between the pea nPAP and PNP, and not to other factors that might copurify with the pea enzyme. These results suggest the existence, in plant nuclei, of factors related to PNP, and an interaction between such factors and poly(A) polymerases.