Overexpression of the single-stranded DNA-binding protein (SSB) stabilises CAG•CTG triplet repeats in an orientation dependent manner

The stability and deletion-size-distribution profiles of leading strand (CAG)75 and (CTG)137 trinucleotide repeat arrays inserted in the Escherichia coli chromosome were investigated upon overexpression of the single-stranded DNA-binding protein (SSB) and in mutant strains deficient for the SbcCD (Rad51/Mre11) nuclease. SSB overexpression increases the stability of the (CAG)75 repeat array and leads to a loss of the bias towards large deletions for the same array. Furthermore, the absence of SbcCD leads to a reduction in the number of large deletions in strains containing the (CTG)137 repeat array.