Cloning and sequencing of LlaDCHI [corrected] restriction/modification genes from Lactococcus lactis and relatedness of this system to the Streptococcus pneumoniae DpnII system.
The natural 7.8-kb plasmid pSRQ700 was isolated from Lactococcus lactis subsp. cremoris DCH-4. It encodes a restriction/modification system named LlaDCHI [corrected]. When introduced into a phage-sensitive L. lactis strain, pSRQ700 confers strong phage resistance against the three most common lactococcal phage species, namely, 936, c2, and P335. The LlaDCHI [corrected] endonuclease was purified and found to cleave the palindromic sequence 5'-GATC-3'. It is an isoschizomer of Streptococcus pneumoniae DpnII. The plasmid pSRQ700 was mapped, and the genetic organization of LlaDCHI [corrected] was localized. Cloning and sequencing of the entire LlaDCHI [corrected] system allowed the identification of three open reading frames. The three genes (llaIIA, llaIIB, and llaIIC) overlapped and are under one putative promoter. A putative terminator was found at the end of llaIIC. The genes llaIIA and llaIIB coded for m6A methyltransferases, and llaIIC coded for an endonuclease. The LlaDCHI [corrected] system shares strong genetic similarities with the DpnII system. The deduced amino acid sequence of M.LlaIIA was 75% identical with that of M.DpnII, whereas M.LlaIIB was 88% identical with M.DpnA. However, R.LlalII shared only 31% identity with R.DpnII.
Moineau
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S
Quest International, Sarasota, Florida 34243, USA.
Walker
S A
SA
Vedamuthu
E R
ER
Vandenbergh
P A
PA
D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D015252:Deoxyribonucleases, Type II Site-Specific / Q000235:genetics*; D013294:Lactococcus lactis / Q000235:genetics*; D008969:Molecular Sequence Data; D016415:Sequence Alignment; D013296:Streptococcus pneumoniae / Q000235:genetics*
D015252:Deoxyribonucleases, Type II Site-Specific; C024405:GATC-specific type II deoxyribonucleases