Petruska J, Arnheim N, Goodman M F
Department of Biological Sciences, Hedco Molecular Biology Laboratories, Molecular Biology Program, University of Southern California, Los Angeles, CA 90089-1340, USA.
Nucleic Acids Res. 1996 Jun 1;24(11):1992-8. doi: 10.1093/nar/24.11.1992.
Expansions of trinucleotide repeats in DNA, a novel source of mutations associated with human disease, may arise by DNA replication slippage initiated by hairpin folding of primer or template strands containing such repeats. To evaluate the stability of single-strand folding by repeating triplets of DNA bases, thermal melting profiles of (CAG)10, (CTG)10, (GAC)10 and (GTC)10 strands are determined at low and physiological salt concentrations, and measurements of melting temperature and enthalpy change are made in each case. Comparisons are made to strands with three times as many repeats, (CAG)30 and (CTG)30. Evidence is presented for stable intrastrand folding by the CAG/CTG class of triplet repeats. Relative to the GAC/GTC class not associated with disease, the order of folding stability is found to be CTG > GAC approximately = CAG > GTC for 10 repeats. Surprisingly, the folds formed by 30 repeats of CTG or CAG have no higher melting temperature and are only 40% more stable in free energy than those formed by 10 repeats. This finding suggests that triplet expansions with higher repeat number may result from the formation of more folded structures with similar stability rather than fewer but longer folds of greater stability.
DNA中三核苷酸重复序列的扩增是与人类疾病相关的一种新的突变来源，它可能由包含此类重复序列的引物或模板链的发夹折叠引发的DNA复制滑动产生。为了评估由DNA碱基三联体重复形成的单链折叠的稳定性，在低盐浓度和生理盐浓度下测定了（CAG）10、（CTG）10、（GAC）10和（GTC）10链的热解链曲线，并分别测量了解链温度和焓变。与重复次数为其三倍的链（CAG）30和（CTG）30进行了比较。结果表明，CAG/CTG类三联体重复可形成稳定的链内折叠。相对于与疾病无关的GAC/GTC类，发现10次重复时的折叠稳定性顺序为CTG > GAC ≈ CAG > GTC。令人惊讶的是，由30次CTG或CAG重复形成的折叠没有更高的解链温度，其自由能稳定性仅比10次重复形成的折叠高40%。这一发现表明，重复次数更高的三联体扩增可能是由形成更多具有相似稳定性的折叠结构导致的，而不是由更少但更长且稳定性更高的折叠导致的。
