pR plasmid replication provides evidence that single-stranded DNA induces the SOS system in vivo.
Evidence is presented that the pR bat gene is essential for plasmid replication and for spontaneous induction of the SOS response in Escherichia coli. Mutations preventing single-stranded DNA production, needed for pR plasmid replication, also prevent the induction of the SOS system. The following experimental design was used. Firstly, we identified the minima rep region, defined as the minimal DNA sequence necessary for pR plasmid replication and, secondly, analyzed the nucleotide sequence of this region. This identified structures and functions (ori-plus, ori-minus and Rep protein) homologous to those found in phages and plasmids replicating by the rolling-circle mechanism. Finally, mutations were introduced either in the replication protein catalytic site or in the nick site consensus sequence, which caused the pR plasmid to lose its ability to induce the SOS system. We conclude that, in this system, the in vivo SOS-inducing signal appears to be the single-stranded DNA produced during pR replication.
Dipartimento di Biopatologia Umana, Università La Sapienza, Policlinico Umberto, Roma, Italy.
F
F
Gigliani
C
C
Ciotta
M F
MF
Del Grosso
P A
PA
Battaglia
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D004261:DNA Replication / Q000235:genetics; D004277:DNA, Single-Stranded / Q000502:physiology*; D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins; D005798:Genes, Bacterial / Q000502:physiology; D008969:Molecular Sequence Data; D010957:Plasmids / Q000502:physiology*; D012093:Replicon; D013014:SOS Response, Genetics / Q000502:physiology*
D001426:Bacterial Proteins; C081232:Bat protein, E coli; D004277:DNA, Single-Stranded; D029968:Escherichia coli Proteins