J. Biol. Chem., Vol. 262, Issue 23, 11167-11175, 08, 1987
Structural organization and DNA methylation patterning within the mouse L1 family
ME Tolberg, SJ Funderburk, I Klisak and SS Smith
We have studied stable differences in patterns of DNA methylation seen in
the repeated sequences of mouse cells. A cloned 1330-base pair fragment of
mouse repetitive DNA (pFS-13) was used as a probe in Southern blotting
experiments. Mouse spleen and L1210 lymphoma DNA appeared to be normally
methylated at HpaII sites probed by this sequence. Friend erythroleukemia
cell, and Sp2 cell DNA both showed an abnormal banding pattern in HpaII
digests. Hybridization in situ to metaphase chromosomes showed that probed
sequences were broadly interspersed along the arms of each mouse
chromosome. The DNA sequence of the 1330-base pair insert in the clone was
determined; a copy of the R sequence of L1 was found at its 5' end. Walking
experiments using M13 subclones from pFS-13 permitted the construction of a
map for d(pCCGG) sites at the 3' end of the mouse L1 family. The
unmethylated d(pCCGG) sites in Sp2 and Friend cells could then be assigned
to polymorphic- repeated sequence groups within L1, homologous to the
region spanned by BAM5 and R. Since there are several thousand copies of
each of the fragments seen in autoradiographs, these sequences must possess
a common methylation state at many genomic locations. Concerted (nonrandom)
hypomethylation of certain subfamilies of L1 appears to be a stable
characteristic of several cell lineages. These findings suggest that
certain L1 families possess commonalities that permit and perhaps require
differential DNA methylation in established cell lineages.
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