<x-flowed>ClaI is subject to methylation at overlapping DAM methylation sites
in DAM+ hosts. Methylation at these sites blocks digestion by ClaI.
The recognition sequence for ClaI is ATCGAT. If this sequence is
preced by a G or followed by a C then a DAM methylation site (GATC)
is present and can be methylated in a DAM+ strain. Since most
strains are DAM+, most BAC DNA will be methylated at these sites.
Sites which are not preceded by a G or followed by a C will still be
digested in DNA deriving from DAM+ strains because they will not be
methylated. There is a good discussion of the different enzymes that
can be affected by DAM methylation in the appendix of the New England
Hope this helps,
Charles S. Gasser, Ph.D.
Section of Molecular and Cellular Biology
University of California
1 Shields Ave.
Davis, CA 95616
csgasser at ucdavis.eduhttp://www-mcb.ucdavis.edu/faculty-labs/gasser/gasser-lab.html
Tel. 530 752-1013
FAX 530 752-3085