Molecular Biology and Evolution, Vol 10, 552-570, Copyright © 1993 by Society for Molecular Biology and Evolution
SA Schichman, NB Adey, MH Edgell and CA Hutchison 3d
LINE-1 (L1) is a family of highly repeated DNA sequences interspersed
throughout the mammalian genome. Individual L1 elements are thought to be
generated by a transposition mechanism involving reverse transcription of
an RNA intermediate followed by insertion into a new genomic site. In mice,
three major families of L1 elements, termed "A," "F," and "V," have been
defined on the basis of the sequence found at the 5' terminus. Previous
analyses of A-monomers have demonstrated sequence heterogeneity among
individual A-monomers, variation in the length of A-monomer sequences, and
the presence of transcriptional regulatory activity. To provide a detailed
characterization of A- monomers as a foundation for studying their
transcriptional regulatory activity, we have analyzed the sequences of 39
complete or partial length A-monomers from 20 different mouse L1 elements.
A-monomers can be classified into six different types according to
shared-sequence length variations. Consensus sequences for the six types of
A-monomers indicate conservation of possible transcription factor-binding
sequences. Specific subgroups of A-monomers correlate with the relative
dispersal time of a mouse L1 element. A phylogenetic analysis of A-
monomers indicates that the length variants represent good diagnostic sites
for phylogenetic subgroups of A-monomer sequences. These observations
suggest a model for the evolution of A-monomer tandem arrays that involves
stepwise mutation and array expansion in the 5' direction. Hybridization
data provide a minimum estimate of 16,000 copies of the A-monomer sequence
in the mouse haploid genome, with an average array length of 2.1 monomer
units.
ORIGINAL ARTICLE
L1 A-monomer tandem arrays have expanded during the course of mouse L1 evolution
Department of Microbiology and Immunology, University of North Carolina, Chapel Hill 27599.
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