Abstract
Gene conversion is a type of homologous recombination that leads to transfer of genetic information among homologous DNA sequences. It can be categorized into two classes: homogenizing and diversifying gene conversions. The former class results in neutralization and homogenization of any sequence variation among repetitive DNA sequences, and thus is important for concerted evolution. On the other hand, the latter functions to increase genetic diversity at the recombination-recipient loci. Thus, these two types of gene conversion play opposite roles in genome dynamics. Diversifying gene conversion is observed in the immunoglobulin (Ig) loci of chicken, rabbit, and other animals, and directs the diversification of Ig variable segments and acquisition of functional Ig repertoires. This type of gene conversion is initiated by the biased occurrence of recombination initiation events (e.g., DNA single- or double-strand breaks) on the recipient DNA site followed by unidirectional homologous recombination from multiple template sequences. Transcription and DNA accessibility is also important in the regulation of biased recombination initiation. In this review, we will discuss the biological significance and possible mechanisms of diversifying gene conversion in somatic cells of eukaryotes.
Highlights
Gene conversion is a type of homologous recombination that leads to transfer of genetic information among homologous DNA sequences
When lesions are introduced into the genomic DNA of somatic cells, DNA breaks must be repaired promptly to prevent chromosomal aberrations or cell death
Homologous recombination is an essential process involved in DNA repair, of DNA-double strand breaks (DSBs)
Summary
Genetic rearrangements play pivotal roles in promoting genetic diversity, and in maintaining genetic integrity. Gene conversion is mainly triggered by DSB formation, followed by the generation of single-stranded DNA tails with free 3' ends. These 3'-end DNA tails invade an intact homologous. The newly synthesized DNA end eventually rehybridizes with the original broken DNA molecule by Watson-Crick base pair interaction This process is called “synthesis-dependent strand annealing (SDSA)” mechanism [1,2,3] (Figure 1). The single strand DNA gap is filled followed by a ligation of DNA nicks In this process, the DNA sequence on the unbroken DNA strand is converted to the broken strand, thereby accompanying a unidirectional transfer of genetic information
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