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Applied and Environmental Microbiology, April 2001, p. 1522-1528, Vol. 67, No. 4
Laboratoire de Génétique et
Microbiologie (INRA UA952), Faculté des Sciences,
Université Henri Poincaré (Nancy 1), 54506 Vandoeuvre-lès-Nancy, France
Received 8 August 2000/Accepted 7 January 2001
A novel type II restriction and modification (R-M) system,
Sth368I, which confers resistance to
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.4.1522-1528.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Characterization of a Novel Type II Restriction-Modification
System, Sth368I, Encoded by the Integrative Element
ICESt1 of Streptococcus thermophilus
CNRZ368
ST84, was found in
Streptococcus thermophilus CNRZ368 but not in the very
closely related strain A054. Partial sequencing of the integrative
conjugative element ICESt1, carried by S. thermophilus CNRZ368 but not by A054, revealed a divergent
cluster of two genes, sth368IR and sth368IM.
The protein sequence encoded by sth368IR is related to the
type II endonucleases R.LlaKR2I and R.Sau3AI,
which recognize and cleave the sequence 5'-GATC-3'. The
protein sequence encoded by sth368IM is very similar to
numerous type II 5-methylcytosine methyltransferases, including M.LlaKR2I and M.Sau3AI. Cell extracts of
CNRZ368 but not A054 were found to cleave at the GATC site.
Furthermore, the C residue of the sequence 5'-GATC-3' was
found to be methylated in CNRZ368 but not in A054. Cloning and
integration of a copy of sth368IR and sth368IM
in the A054 chromosome confers on this strain phenotypes similar to those of CNRZ368, i.e., phage resistance, endonuclease activity of cell extracts, and methylation of the sequence
5'-GATC-3'. Disruption of sth368IR removes
resistance and restriction activity. We conclude that
ICESt1 encodes an R-M system, Sth368I, which recognizes the sequence 5'-GATC-3' and is related to
the Sau3AI and LlaKR2I restriction systems.
*
Corresponding author. Mailing address: Laboratoire de
Génétique et Microbiologie (INRA UA952), Faculté des
Sciences, Université Henri Poincaré (Nancy 1), BP239, 54506 Vandoeuvre-lès-Nancy, France. Phone: (33) 3 83 91 21 93. Fax:
(33) 3 83 91 25 00. E-mail: decaris{at}nancy.inra.fr.
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