TY - JOUR
T1 - DNA tandem repeat instability in the Escherichia coli chromosome is stimulated by mismatch repair at an adjacent CAG·CTG trinucleotide repeat
AU - Blackwood, John K.
AU - Okely, Ewa A.
AU - Zahra, Rabaab
AU - Eykelenboom, John K.
AU - Leach, David R. F.
PY - 2010/12/28
Y1 - 2010/12/28
N2 - Approximately half the human genome is composed of repetitive DNA sequences classified into microsatellites, minisatellites, tandem repeats, and dispersed repeats. These repetitive sequences have coevolved within the genome but little is known about their potential interactions. Trinucleotide repeats (TNRs) are a subclass of microsatellites that are implicated in human disease. Expansion of CAG.CTG TNRs is responsible for Huntington disease, myotonic dystrophy, and a number of spinocerebellar ataxias. In yeast DNA double-strand break (DSB) formation has been proposed to be associated with instability and chromosome fragility at these sites and replication fork reversal (RFR) to be involved either in promoting or in preventing instability. However, the molecular basis for chromosome fragility of repetitive DNA remains poorly understood. Here we show that a CAG.CTG TNR array stimulates instability at a 275-bp tandem repeat located 6.3 kb away on the Escherichia coli chromosome. Remarkably, this stimulation is independent of both DNA double-strand break repair (DSBR) and RFR but is dependent on a functional mismatch repair (MMR) system. Our results provide a demonstration, in a simple model system, that MMR at one type of repetitive DNA has the potential to influence the stability of another. Furthermore, the mechanism of this stimulation places a limit on the universality of DSBR or RFR models of instability and chromosome fragility at CAG.CTG TNR sequences. Instead, our data suggest that explanations of chromosome fragility should encompass the possibility of chromosome gaps formed during MMR.
AB - Approximately half the human genome is composed of repetitive DNA sequences classified into microsatellites, minisatellites, tandem repeats, and dispersed repeats. These repetitive sequences have coevolved within the genome but little is known about their potential interactions. Trinucleotide repeats (TNRs) are a subclass of microsatellites that are implicated in human disease. Expansion of CAG.CTG TNRs is responsible for Huntington disease, myotonic dystrophy, and a number of spinocerebellar ataxias. In yeast DNA double-strand break (DSB) formation has been proposed to be associated with instability and chromosome fragility at these sites and replication fork reversal (RFR) to be involved either in promoting or in preventing instability. However, the molecular basis for chromosome fragility of repetitive DNA remains poorly understood. Here we show that a CAG.CTG TNR array stimulates instability at a 275-bp tandem repeat located 6.3 kb away on the Escherichia coli chromosome. Remarkably, this stimulation is independent of both DNA double-strand break repair (DSBR) and RFR but is dependent on a functional mismatch repair (MMR) system. Our results provide a demonstration, in a simple model system, that MMR at one type of repetitive DNA has the potential to influence the stability of another. Furthermore, the mechanism of this stimulation places a limit on the universality of DSBR or RFR models of instability and chromosome fragility at CAG.CTG TNR sequences. Instead, our data suggest that explanations of chromosome fragility should encompass the possibility of chromosome gaps formed during MMR.
KW - DNA repair
KW - DNA replication
KW - fragile site
UR - http://www.scopus.com/inward/record.url?scp=78651090023&partnerID=8YFLogxK
U2 - 10.1073/pnas.1012906108
DO - 10.1073/pnas.1012906108
M3 - Article
SN - 0027-8424
VL - 107
SP - 22582
EP - 22586
JO - Proceedings of the National Academy of Sciences (PNAS)
JF - Proceedings of the National Academy of Sciences (PNAS)
IS - 52
ER -