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Journal of Bacteriology, November 1998, p. 5844-5854, Vol. 180, No. 22
Department of Food Science and Nutrition,
University of Minnesota, St. Paul, Minnesota 55108
Received 6 March 1998/Accepted 4 September 1998
The nucleotide sequence of the plasmid-encoded LlaKR2I
restriction-modification (R-M) system of Lactococcus lactis
subsp. lactis biovar diacetylactis KR2 was determined. This
R-M system comprises divergently transcribed endonuclease
(llaKR2IR) and methyltransferase (llaKR2IM)
genes; located in the intergenic region is a copy of the insertion
element IS982, whose putative transposase gene is
codirectionally transcribed with llaKR2IM. The deduced
sequence of the LlaKR2I endonuclease shared homology with
the type II endonuclease Sau3AI and with the MutH mismatch repair protein, both of which recognize and cleave the sequence 5' GATC
3'. In addition, M · LlaKR2I displayed homology
with the 5-methylcytosine methyltransferase family of proteins,
exhibiting greatest identity with M · Sau3AI. Both
of these proteins shared notable homology throughout their putative
target recognition domains. Furthermore, subclones of the native
parental lactococcal plasmid pKR223, which encode
M · LlaKR2I, all remained undigested after
treatment with Sau3AI despite the presence of multiple 5' GATC 3' sites. The combination of these data suggested that the specificity of the LlaKR2I R-M system was likely to be 5'
GATC 3', with the cytosine residue being modified to 5-methylcytosine. The IS982 element located within the LlaKR2I
R-M system contained at its extremities two 16-bp perfect inverted
repeats flanked by two 7-bp direct repeats. A perfect extended promoter
consensus, which represented the likely original promoter of the
llaKR2IR gene, was shown to overlap the direct repeat
sequence on the other side of IS982. Specific deletion of
IS982 and one of these direct repeats via a PCR strategy
indicated that the LlaKR2I R-M determinants do not rely on
elements within IS982 for expression and that the efficiency of bacteriophage restriction was not impaired.
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Molecular Characterization of the Lactococcus
lactis LlaKR2I Restriction-Modification System and Effect of an
IS982 Element Positioned between the Restriction and
Modification Genes

*
Corresponding author. Mailing address: Department of
Food Science and Nutrition, 1334 Eckles Ave., St. Paul, MN 55108. Phone: (612) 624-5335. Fax: (612) 625-5272. E-mail:
osull001{at}tc.umn.edu.
Paper no. 981180025 of the Scientific Journal Series of the
Minnesota Agricultural Experiment Station.
Present address: Dairy Quality Department, Teagasc, National Dairy
Products Research Center, Moorepark, Fermoy, Co. Cork, Ireland.
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