Distribution of poly(A) polymerase I in bacteria: an expanded role for horizontal gene transfer.

Poly(A) polymerase I (PAP I), the product of the pcnB gene, catalyses the polyadenylation of RNA 3'-ends in Escherichia coli. PAP I and pcnB were initially thought to be present only in the β, γ-Proteobacteria and a few other bacterial species. In the present study, blast searches using bacterial proteins bearing the PAP I signature sequence as queries have revealed the presence of proteins containing that signature sequence in a wide range of additional bacterial classes and phyla. Phylogenetic studies indicate that the pcnB genes in most of these newly identified species were not inherited by horizontal gene transfer (HGT) from β, γ-proteobacterial donors. Nevertheless, the present studies reveal a larger role for HGT in the inheritance of pcnB genes than was documented in previous studies. Together with the other studies cited here, the results presented below strongly suggest that the significant metabolic role for the polyadenylation of RNA 3'-ends in the domain Bacteria.