title: Functional characterization of the type II PamI restriction-modification system derived from plasmid pAMI7 of Paracoccus aminophilus JCM 7686.
abstract: Plasmid pAMI7 of the methylotrophic bacterium Paracoccus aminophilus JCM 7686 (Alphaproteobacteria) encodes a functional type II restriction-modification (R-M) system designated PamI. Homologous systems were identified in the genomes of distinct taxonomic groups of Bacteria and Archaea, which provides evidence that horizontal gene transfer has contributed to the wide dissemination of R-M modules - even between domains. Analysis of the cleavage specificity of the R.PamI endonuclease revealed that this protein is an isoschizomer of restriction enzyme NcoI. Interestingly, bioinformatic analyses suggest that R.PamI and NcoI are accompanied by methyltransferases of different methylation specificities (C5-methylcytosine and N4-methylcytosine methyltransferases, respectively), which possibly exemplifies recombinational shuffling of genes coding for individual components of R-M systems. The PamI system can stabilize plasmid pAMI7 in a bacterial population, most probably at the postsegregational level. Therefore, it functions in an analogous manner to plasmid-encoded toxin-antitoxin (TA) systems. Since the TA system of pAMI7 is nonfunctional, it is highly probable that this lack is compensated by the stabilizing activity of PamI. This indicates the crucial role of the analyzed R-M system in the stable maintenance of pAMI7, which is, to our knowledge, the first report of 'symbiosis' between a R-M system and a plasmid in the Alphaproteobacteria.
authors.affiliation: Department of Bacterial Genetics, Faculty of Biology, Institute of Microbiology, University of Warsaw, Warsaw, Poland. ldziewit@biol.uw.edu.pl
authors.forename: Lukasz
authors.initials: L
authors.lastname: Dziewit
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Kuczkowska
authors.forename: Marcin
authors.initials: M
authors.lastname: Adamczuk
authors.forename: Monika
authors.initials: M
authors.lastname: Radlinska
authors.forename: Dariusz
authors.initials: D
authors.lastname: Bartosik
mesh_terms: D000595:Amino Acid Sequence; D004247:DNA / Q000378:metabolism; D015280:DNA Restriction-Modification Enzymes / Q000235:genetics* / Q000378:metabolism*; D015252:Deoxyribonucleases, Type II Site-Specific / Q000235:genetics* / Q000378:metabolism*; D022761:Gene Transfer, Horizontal; D008969:Molecular Sequence Data; D010230:Paracoccus / Q000201:enzymology* / Q000235:genetics*; D010957:Plasmids; D017385:Sequence Homology; D013379:Substrate Specificity
chemical_list: D015280:DNA Restriction-Modification Enzymes; D004247:DNA; C073083:endodeoxyribonuclease MstI; D015252:Deoxyribonucleases, Type II Site-Specific