title: The DpnI/DpnII pneumococcal system, defense against foreign attack without compromising genetic exchange.
abstract: Natural genetic transformation and restriction-modification (R-M) systems play potentially antagonistic roles in bacteria. R-M systems, degrading foreign DNA to protect the cell from bacteriophage, can interfere with transformation, which relies on foreign DNA to promote genetic diversity. Here we describe how the human pathogenStreptococcus pneumoniae, which is naturally transformable, yet possesses either of two R-M systems, DpnI or DpnII, accommodates these conflicting processes. In addition to the classic restrictase and double-stranded DNA methylase, the DpnII system possesses an unusual single-stranded (ss) DNA methylase, DpnA, which is specifically induced during competence for genetic transformation. We provide further insight into our recent discovery that DpnA, which protects transforming foreign ssDNA from restriction, is crucial for acquisition of pathogenicity islands.
authors.affiliation: Centre National de la Recherche Scientifique; LMGM-UMR5100; Toulouse, France ; Laboratoire de Microbiologie et Génétique Moléculaires; Université de Toulouse; UPS; Toulouse, France.
authors.forename: Calum
authors.initials: C
authors.lastname: Johnston
authors.forename: Patrice
authors.initials: P
authors.lastname: Polard
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Claverys
keywords: DpnA ssDNA methylase; Streptococcus pneumoniae; capsule switch; competence; genetic transformation; heterologous DNA transfer; pathogenicity island transfer; restriction–modification