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Title: Single-Stranded Annealing Induced by Re-Initiation of Replication Origins Provides a Novel and Efficient Mechanism for Generating Copy Number Expansion via Non-Allelic Homologous Recombination.      
keywords:
Variation
ID:
PRJNA176386
description:
Copy number expansions such as amplifications and duplications contribute to human phenotypic variation, promote molecular diversification during evolution, and drive the initiation and/or progression of various cancers. The mechanisms underlying these copy number changes are still incompletely understood, however. We recently demonstrated that transient, limited re-replication from a single origin in Saccharomyces cerevisiae efficiently induces segmental amplification of the re-replicated region. Structural analyses of such re-replication induced gene amplifications (RRIGA) suggested that RRIGA could provide a new mechanism for generating copy number variation by non-allelic homologous recombination (NAHR). Here we elucidate this new mechanism and provide insight into why it is so efficient. We establish that sequence homology is both necessary and sufficient for repetitive elements to participate in RRIGA and show that their recombination occurs by a single-strand annealing (SSA) mechanism. We also find that re-replication forks are prone to breakage, accounting for the widespread DNA damage associated with deregulation of replication proteins. These breaks appear to stimulate NAHR between re-replicated repeat sequences flanking a re-initiating replication origin. Our results support a RRIGA model where the expansion of a re-replication bubble beyond flanking homologous sequences followed by breakage at both forks in trans provides an ideal structural context for SSA–mediated NAHR to form a head-to-tail duplication. Given the remarkable efficiency of RRIGA, we suggest it may be an unappreciated contributor to copy number expansions in both disease and evolution. Overall design: The arrays in this series are primary comparative genomic hybridizations to determine genomic changes after re-replication. Genomic DNA was purified from reference Saccharomyces cerevisiae cells or survivors of re-replication, differentially labeled with Cy3 and Cy5, and competitively hybridized to a spotted microarray containing ORF and intergenic PCR products. Cy5/Cy3 ratios (or the inverse in the case of dye swapped samples) are normalized so that the average ratio of all elements was 1 (except for arrays measuring re-replication induction where this ratio was set to 2). A small number of the arrays were used to determine the extent and location of re-replication under different conditions. For those, genomic DNA was purified from non-replicating and re-replicating cells and treated as above. Series contains a total of 333 hybridizations. Note that the VALUE field reported for all of the sample tables in this series are the log2 of the normalized Cy5/Cy3 (or Cy3/Cy5) ratio. To convert these into usable copy number profiles raise 2 to the indicated VALUE.
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landingpage: http://www.ncbi.nlm.nih.gov/bioproject/PRJNA176386
authentication:
none
authorization:
none
ID:
pmid:23300490
name:
Saccharomyces cerevisiae
ncbiID:
ncbitax:4932
abbreviation:
NCBI
homePage: http://www.ncbi.nlm.nih.gov
ID:
SCR:006472
name:
National Center for Biotechnology Information
homePage: http://www.ncbi.nlm.nih.gov/bioproject
ID:
SCR:004801
name:
NCBI BioProject