Prokaryotes protect their genomes from foreign DNA with a diversity of defence mechanisms, including a widespread restriction-modification (R-M) system involving phosphorothioate (PT) modification of the DNA backbone. Unlike classical R-M systems, highly partial PT modification of consensus motifs in bacterial genomes suggests an unusual mechanism of PT-dependent restriction. In Salmonella ente...

Restriction-modification systems consist of a modification enzyme that methylates a specific DNA sequence and a restriction endonuclease that cleaves DNA lacking this epigenetic signature. Their gene expression should be finely regulated because their potential to attack the host bacterial genome needs to be controlled. In the EcoRI system, where the restriction gene is located upstream of the ...

Esp1396I restriction-modification (RM) system recognizes an interrupted palindromic DNA sequence 5'-CCA(N)(5)TGG-3'. The Esp1396I RM system was found to reside on pEsp1396, a 5.6 kb plasmid naturally occurring in Enterobacter sp. strain RFL1396. The nucleotide sequence of the entire 5622 bp pEsp1396 plasmid was determined on both strands. Identified genes for DNA methyltransferase (esp1396IM) a...

The Restriction-modification system AhdI contains two convergent transcription units, one with genes encoding methyltransferase subunits M and S and another with genes encoding the controller (C) protein and the restriction endonuclease (R). We show that AhdI transcription is controlled by two independent regulatory loops that are well-optimized to ensure successful establishment in a naïve bac...

When a plasmid containing restriction-modification (R-M) genes enters a naïve host, unmodified host DNA can be destroyed by restriction endonuclease. Therefore, expression of R-M genes must be regulated to ensure that enough methyltransferase is produced and that host DNA is methylated before the endonuclease synthesis begins. In several R-M systems, specialized Control (C) proteins coordinate ...

Three genes coding for the endonuclease, methylase, and specificity subunits of a type I restriction-modification (R-M) system in the Lactococcus lactis plasmid pIL2614 have been characterized. Plasmid location, sequence homologies, and inactivation studies indicated that this R-M system is most probably of type IC.

The two genes encoding the class IIS restriction-modification system MboII from Moraxella bovis were cloned separately in two compatible plasmids and expressed in E. coli RR1 delta M15. The nucleotide sequences of the MboII endonuclease (R.MboII) and methylase (M.MboII) genes were determined and the putative start codon of R.MboII was confirmed by amino acid sequence analysis. The mboIIR gene s...