SOS repair and DNA supercoiling influence the genetic stability of DNA triplet repeats in Escherichia coli.
Molecular mechanisms responsible for the genetic instability of DNA trinucleotide sequences (TRS) account for at least 20 human hereditary disorders. Many aspects of DNA metabolism influence the frequency of length changes in such repeats. Herein, we demonstrate that expression of Escherichia coli SOS repair proteins dramatically decreases the genetic stability of long (CTG/CAG)n tracts contained in plasmids. Furthermore, the growth characteristics of the bacteria are affected by the (CTG/CAG)n tract, with the effect dependent on the length of the TRS. In an E. coli host strain with constitutive expression of the SOS regulon, the frequency of deletions to the repeat is substantially higher than that in a strain with no SOS response. Analyses of the topology of reporter plasmids isolated from the SOS+ and SOS- strains revealed higher levels of negative supercoiling in strains with the constitutively expressed SOS network. Hence, we used strains with mutations in topoisomerases to examine the effect of DNA topology upon the TRS instability. Higher levels of negative DNA supercoiling correlated with increased deletions in long (CTG/CAG)n, (CGG/CCG)n and (GAA/TTC)n. These observations suggest a link between the induction of bacterial SOS repair, changes in DNA topology and the mechanisms leading to genetic instability of repetitive DNA sequences.
Majchrzak
Marta
M
Centre for Medical Biology, Polish Academy of Sciences, 106 Lodowa Street, 93-232 Lodz, Poland.
Bowater
Richard P
RP
Staczek
Pawel
P
Parniewski
Pawel
P
D004247:DNA / Q000378:metabolism; D004269:DNA, Bacterial / Q000235:genetics; D004278:DNA, Superhelical; D004926:Escherichia coli / Q000235:genetics*; D010957:Plasmids / Q000235:genetics; D013014:SOS Response, Genetics; D017384:Sequence Deletion; D018911:Trinucleotide Repeats
D004269:DNA, Bacterial; D004278:DNA, Superhelical; D004247:DNA