title: [Cloning and structure analysis of a restriction and modification system, LlaBIII from Lactococcus lactis subsp. cremoris W56].
abstract: A 22.4 kb naturally occurring plasmid pJW566, isolated from L. lactis W56, was found to encode an R/M system named LlaBIII. The LlaBIII R/M system was isolated on a chloramphenicol resistant derivative of plasmid pJW566, resulting in a plasmid pJK1. Subcloning analysis showed that the LlaBIII determinant was located on a 5 kb HindIII-Sph I fragment. The fragment was sequenced. It contained a single open reading frame (ORF), corresponding to a protein of 1584 or 1576 aa. In the deduced amino acid sequence seven helicase motifs characteristic of endonuclease type I and type III and a conserved catalysis motif X in the R subunits of type I R/M systems were located in the N-terminus, followed by four conserved motifs found in DNA N6-adenine methyltransferases. The C-terminus of the deduced amino acid sequence showed no homology to known R/M systems. Therefore, this polypeptide encoded by LlaBIII is a multifunctional protein possessing putative DNA recognition, methylation and restriction activities.
authors.affiliation: State Key Laboratory of Microbial Technology, Shandong University, Jinan 250100, China. kongjian@sdu.edu.cn
authors.forename: J
authors.initials: J
authors.lastname: Kong
authors.forename: J
authors.initials: J
authors.lastname: Jytte
authors.forename: G R
authors.initials: GR
authors.lastname: Ma
mesh_terms: D003001:Cloning, Molecular; D015254:DNA Modification Methylases / Q000737:chemistry*; D015280:DNA Restriction-Modification Enzymes / Q000737:chemistry* / Q000235:genetics; D043224:Deoxyribonuclease (Pyrimidine Dimer); D003850:Deoxyribonuclease I / Q000737:chemistry*; D004706:Endodeoxyribonucleases / Q000737:chemistry; D029968:Escherichia coli Proteins; D013294:Lactococcus lactis / Q000201:enzymology* / Q000235:genetics; D009097:Multienzyme Complexes / Q000737:chemistry / Q000235:genetics; D010957:Plasmids; D017386:Sequence Homology, Amino Acid
chemical_list: D015280:DNA Restriction-Modification Enzymes; D029968:Escherichia coli Proteins; D009097:Multienzyme Complexes; D015254:DNA Modification Methylases; D004706:Endodeoxyribonucleases; D003850:Deoxyribonuclease I; D043224:Deoxyribonuclease (Pyrimidine Dimer); C106403:NTH protein, E coli