Abstract
Restriction enzyme analysis of normal DNA derived from individual
rats of the National Institutes of Health outbred Osborn-Mendel colony
revealed that two independent single-copy loci, the Igh (immunoglobulin
heavy chain) locus and the Mlvi-2 (Moloney leukemia virus integration
2) locus, a putative oncogene, are polymorphic (i.e., exhibit allelic
variation). The polymorphism at both loci was due to the presence
or absence of a long interspersed repeated DNA element (LINE). The
LINE insertion in the Igh locus occurred in the joining (J) region,
which is involved in the physiological rearrangement of this locus.
The LINE insertion in the Mlvi-2 locus has occurred approximately
6 kilobases from the region of provirus integration in Moloney murine
leukemia virus-induced rat thymomas. The two inserts are colinear
with each other and with other randomly selected cloned copies of
the rat LINE family, the general characteristics of which we also
present. LINE insertion in the Mlvi-2 locus was observed in several
rat strains, established from independent rat colonies, suggesting
that LINE-containing Mlvi-2 alleles may be widespread in the rat
population. LINE insertion in the Igh locus was observed in 1 of
27 rats. The detection of a LINE-related polymorphism at two nonselected
loci indicates that LINEs are transposable. The presence or absence
of these long (greater than 5 kilobases), highly transcribed elements
at single-copy loci could have profound effects on gene activity.
Furthermore, LINE-containing single-copy loci could be affected by
homologous interaction between the resident LINE and any of the other
50,000 or so copies of these elements in the rat genome.
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