title: Cloning and characterization of the lactococcal plasmid-encoded type II restriction/modification system, LlaDII.
abstract: The LlaDII restriction/modification (R/M) system was found on the naturally occurring 8.9-kb plasmid pHW393 in Lactococcus lactis subsp. cremoris W39. A 2.4-kb PstI-EcoRI fragment inserted into the Escherichia coli-L. lactis shuttle vector pCI3340 conferred to L. lactis LM2301 and L. lactis SMQ86 resistance against representatives of the three most common lactococcal phage species: 936, P335, and c2. The LlaDII endonuclease was partially purified and found to recognize and cleave the sequence 5'-GC decreases NGC-3', where the arrow indicates the cleavage site. It is thus an isoschizomer of the commercially available restriction endonuclease Fnu4HI. Sequencing of the 2.4-kb PstI-EcoRI fragment revealed two open reading frames arranged tandemly and separated by a 105-bp intergenic region. The endonuclease gene of 543 bp preceded the methylase gene of 954 bp. The deduced amino acid sequence of the LlaDII R/M system showed high homology to that of its only sequenced isoschizomer, Bsp6I from Bacillus sp. strain RFL6, with 41% identity between the endonucleases and 60% identity between the methylases. The genetic organizations of the LlaDII and Bsp6I R/M systems are identical. Both methylases have two recognition sites (5'-GCGGC-3' and 5'-GCCGC-3') forming a putative stemloop structure spanning part of the presumed -35 sequence and part of the intervening region between the -35 and -10 sequences. Alignment of the LlaDII and Bsp6I methylases with other m5C methylases showed that the protein primary structures possessed the same organization.
authors.affiliation: Department of Dairy and Food Science, Royal Veterinary and Agricultural University, Frederiksberg, Denmark.
authors.forename: A
authors.initials: A
authors.lastname: Madsen
authors.forename: J
authors.initials: J
authors.lastname: Josephsen
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D003001:Cloning, Molecular; D015257:DNA-Cytosine Methylases / Q000235:genetics*; D015252:Deoxyribonucleases, Type II Site-Specific / Q000235:genetics*; D004706:Endodeoxyribonucleases / Q000235:genetics*; D013294:Lactococcus lactis / Q000201:enzymology*; D008969:Molecular Sequence Data; D010957:Plasmids / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; C094486:Bsp6I methyltransferase, Bacillus sp.; D015257:DNA-Cytosine Methylases; D004706:Endodeoxyribonucleases; C113512:endodeoxyribonuclease LlaDII; D015252:Deoxyribonucleases, Type II Site-Specific