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9647810
Cloning and characterization of the lactococcal plasmid-encoded type II restriction/modification system, LlaDII.

Appl Environ Microbiol, 1998/7;64(7):2424-31.

Madsen A[1], Josephsen J

Affiliations

PMID: 9647810

Impact factor: 5.005

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.
MeSH terms
Amino Acid Sequence; Bacterial Proteins; Base Sequence; Cloning, Molecular; DNA-Cytosine Methylases; Deoxyribonucleases, Type II Site-Specific; Endodeoxyribonucleases; Lactococcus lactis; Molecular Sequence Data; Plasmids
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