Lyamichev V I, Mirkin S M, Danilevskaya O N, Voloshin O N, Balatskaya S V, Dobrynin V N, Filippov S A, Frank-Kamenetskii M D
Institute of Molecular Genetics, USSR Academy of Sciences, Moscow.
Nature. 1989 Jun 22;339(6226):634-7. doi: 10.1038/339634a0.
Telomeric sequences of DNA, which are found at the ends of linear chromosomes, have been attracting attention as potential sites for the formation of unusual DNA structures. They consist of (GnTm) or (GnATm) motifs (n greater than or equal to m) and, in the single-stranded state, form hairpins stabilized by non-canonical G.G pairs. In the duplex state and under superhelical stress they exhibit hypersensitivity to SI nuclease which by analogy with homopurine-homopyrimidine sequences may reflect the formation of an unusual structure. To determine whether this is the case we have inserted into a plasmid the Tetrahymena telomeric motif (G4T2).(A2C4) and probed it by two-dimensional gel electrophoresis, chemical modification and oligonucleotide binding. Our data demonstrate that, under superhelical stress and at low pH, the insert does indeed adopt a novel DNA conformation. We have concluded that in this structure the C-rich strand forms a hairpin stabilized by non-Watson-Crick base pairs C.C+ and A.A+, whereas the G-rich strand remains unstructured. We term this new DNA structure the (C,A)-hairpin.
端粒DNA序列位于线性染色体末端，作为形成异常DNA结构的潜在位点一直备受关注。它们由（GnTm）或（GnATm）基序组成（n大于或等于m），在单链状态下形成由非经典G.G碱基对稳定的发夹结构。在双链状态和超螺旋应力下，它们对SI核酸酶表现出超敏性，类似于同嘌呤-同嘧啶序列，这可能反映了异常结构的形成。为了确定是否如此，我们将四膜虫端粒基序（G4T2）.（A2C4）插入质粒，并通过二维凝胶电泳、化学修饰和寡核苷酸结合进行检测。我们的数据表明，在超螺旋应力和低pH条件下，插入片段确实采用了一种新的DNA构象。我们得出结论，在这种结构中，富含C的链形成由非沃森-克里克碱基对C.C+和A.A+稳定的发夹结构，而富含G的链保持无结构状态。我们将这种新的DNA结构称为（C，A）-发夹结构。
