Factors affecting ectopic gene conversion in mice |
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Authors: | Deoborah M Cooper Kerry J Schimenti John C Schimenti |
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Institution: | (1) The Jackson Laboratory, Bar Harbor, Maine 04609, USA, US |
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Abstract: | Duplicated genes and repetitive sequences are distributed throughout the genomes of complex organisms. The homology between
related sequences can promote nonallelic (ectopic) recombination, including gene conversion and reciprocal exchange. Resolution
of these events can result in translocations, deletions, or other harmful rearrangements. In yeast, ectopic recombination
between sequences on nonhomologous chromosomes occurs at high frequency. Because the mammalian genome is replete with duplicated
sequences and repetitive elements, high levels of ectopic exchange would cause aneuploidy and genome instability. To understand
the factors regulating ectopic recombination in mice, we evaluated the effects of homology length on gene conversion between
unlinked sequences in the male germline. Previously, we found high levels of gene conversion between lacZ transgenes containing 2557 bp of homology. We report here that genetic background can play a major role in ectopic recombination;
frequency of gene conversion was reduced by more than an order of magnitude by transferring the transgenes from a CF1 strain
background to C57BL/6J. Additionally, conversion rates decreased as the homology length decreased. Sequences sharing 1214
bp of sequence identity underwent ectopic conversion less frequently than a pair sharing 2557 bp of identity, while 624 bp
was insufficient to catalyze gene conversion at significant levels. These results suggest that the germline recombination
machinery in mammals has evolved in a way that prevents high levels of ectopic recombination between smaller classes of repetitive
sequences, such as the Alu family. Additionally, genomic location appeared to influence the availability of sequences for ectopic recombination.
Received: 12 September 1997 / Accepted: 29 December 1997 |
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