title: Phase variation of Enterococcus faecalis pAD1 conjugation functions relates to changes in iteron sequence region.
abstract: pAD1 (60 kb) is a conjugative, hemolysin/bacteriocin plasmid in Enterococcus faecalis. It confers a mating response to the peptide sex pheromone cAD1 produced by recipient (plasmid-free) cells, leading to highly efficient plasmid transfer in broth matings. Control of the physiological response to cAD1 can been overridden by a reversible phase variation event at frequencies on the order of 10(-4) to 10(-3) per cell per generation (L. T. Pontius and D. B. Clewell, Plasmid 26:172-185, 1991). The variant forms are designated Dryc and Dry+, which reflects the colony morphologies of cells whose conjugation functions are switched on and off, respectively. Here we show that Dryc variants exhibit a structural change in a region between repA and repB that contains two clusters of 8-bp iterons. The change involved a 31- or 32-bp increase in size of this region. In three or four independent variants examined, one of the iteron clusters increased in size from 13 to 17 iterons. When iteron DNA was placed on a multicopy plasmid and introduced into a wild-type pAD1 derivative, the Dryc phenotype was generated. Since traA, a key negative regulator of conjugation, bears several centrally located iteron-like sequences with the same orientation, we speculate that the protein(s) that normally binds iterons (possibly RepA and/or RepB) blocks traA transcription in Dryc variants.
authors.affiliation: Department of Biologic and Materials Sciences, School of Dentistry, University of Michigan, Ann Arbor 48109, USA.
authors.forename: D G
authors.initials: DG
authors.lastname: Heath
authors.forename: F Y
authors.initials: FY
authors.lastname: An
authors.forename: K E
authors.initials: KE
authors.lastname: Weaver
authors.forename: D B
authors.initials: DB
authors.lastname: Clewell
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D003227:Conjugation, Genetic / Q000235:genetics*; D004265:DNA Helicases; D004268:DNA-Binding Proteins; D013293:Enterococcus faecalis / Q000235:genetics* / Q000502:physiology; D036781:Fimbriae Proteins; D005798:Genes, Bacterial / Q000235:genetics; D008969:Molecular Sequence Data; D010957:Plasmids / Q000235:genetics*; D011506:Proteins; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics*; D015534:Trans-Activators
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D011506:Proteins; C048817:RepB protein, Bacteria; D015534:Trans-Activators; C045264:replication initiator protein; C082576:traB protein, Bacteria; C074790:traC protein, Plasmid F; D036781:Fimbriae Proteins; D004265:DNA Helicases