title: Polynucleotide phosphorylase is implicated in homologous recombination and DNA repair in Escherichia coli.
abstract: Polynucleotide phosphorylase (PNPase, encoded by pnp) is generally thought of as an enzyme dedicated to RNA metabolism. The pleiotropic effects of PNPase deficiency is imputed to altered processing and turnover of mRNAs and small RNAs, which in turn leads to aberrant gene expression. However, it has long since been known that this enzyme may also catalyze template-independent polymerization of dNDPs into ssDNA and the reverse phosphorolytic reaction. Recently, PNPase has been implicated in DNA recombination, repair, mutagenesis and resistance to genotoxic agents in diverse bacterial species, raising the possibility that PNPase may directly, rather than through control of gene expression, participate in these processes.
  
  
  
  In this work we present evidence that in Escherichia coli PNPase enhances both homologous recombination upon P1 transduction and error prone DNA repair of double strand breaks induced by zeocin, a radiomimetic agent. Homologous recombination does not require PNPase phosphorolytic activity and is modulated by its RNA binding domains whereas error prone DNA repair of zeocin-induced DNA damage is dependent on PNPase catalytic activity and cannot be suppressed by overexpression of RNase II, the other major enzyme (encoded by rnb) implicated in exonucleolytic RNA degradation. Moreover, E. coli pnp mutants are more sensitive than the wild type to zeocin. This phenotype depends on PNPase phosphorolytic activity and is suppressed by rnb, thus suggesting that zeocin detoxification may largely depend on RNA turnover.
  
  
  
  Our data suggest that PNPase may participate both directly and indirectly through regulation of gene expression to several aspects of DNA metabolism such as recombination, DNA repair and resistance to genotoxic agents.
authors.affiliation: Dipartimento di Bioscienze, Università degli Studi di Milano, via Celoria 26, Milan, 20133, Italy.|Present address: Dipartimento di Biotecnologie mediche e medicina traslazionale, Università degli Studi di Milano, via F.lli Cervi 93, Segrate, MI, 20090, Italy.
authors.forename: Thomas
authors.initials: T
authors.lastname: Carzaniga
authors.affiliation: Dipartimento di Bioscienze, Università degli Studi di Milano, via Celoria 26, Milan, 20133, Italy.|Present address: Eurofins BioPharma Product Testing Italy, Eurofins Biolab srl, via Bruno Buozzi, 2, Vimodrone, 20090, Italy.
authors.forename: Giulia
authors.initials: G
authors.lastname: Sbarufatti
authors.affiliation: Dipartimento di Bioscienze, Università degli Studi di Milano, via Celoria 26, Milan, 20133, Italy.
authors.forename: Federica
authors.initials: F
authors.lastname: Briani
authors.affiliation: Dipartimento di Bioscienze, Università degli Studi di Milano, via Celoria 26, Milan, 20133, Italy. gianni.deho@unimi.it.
authors.forename: Gianni
authors.identifier: 0000-0001-5492-7766
authors.initials: G
authors.lastname: Dehò
mesh_terms: D001761:Bleomycin / Q000494:pharmacology; D004249:DNA Damage; D004260:DNA Repair; D004277:DNA, Single-Stranded / Q000378:metabolism; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D005095:Exoribonucleases / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D015971:Gene Expression Regulation, Enzymologic; D059765:Homologous Recombination; D016296:Mutagenesis; D009154:Mutation; D011117:Polyribonucleotide Nucleotidyltransferase / Q000235:genetics* / Q000378:metabolism*; D011485:Protein Binding; D020871:RNA Stability; D012329:RNA, Bacterial; D012333:RNA, Messenger / Q000378:metabolism
chemical_list: D004277:DNA, Single-Stranded; D029968:Escherichia coli Proteins; D012329:RNA, Bacterial; D012333:RNA, Messenger; D001761:Bleomycin; C105427:Zeocin; D011117:Polyribonucleotide Nucleotidyltransferase; D005095:Exoribonucleases; C022535:exoribonuclease II
keywords: DNA repair; Genetic recombination; Mutagenesis; Polynucleotide phosphorylase; RNA metabolism