i-Motif (iM) is a four stranded DNA structure formed by cytosine-rich sequences, which are often present in functionally important parts of the genome such as promoters of genes and telomeres. Using electronic circular dichroism and UV absorption spectroscopies and electrophoretic methods, we examined the effect of four naturally occurring DNA base lesions on the folding and stability of the iM formed by the human telomere DNA sequence (C₃TAA)₃C₃T. The results demonstrate that the TAA loop lesions, the apurinic site and 8-oxoadenine substituting for adenine, and the 5-hydroxymethyluracil substituting for thymine only marginally disturb the formation of iM. The presence of uracil, which is formed by enzymatic or spontaneous deamination of cytosine, shifts iM formation towards substantially more acidic pH values and simultaneously distinctly reduces iM stability. This effect depends on the position of the damage sites in the sequence. The results have enabled us to formulate additional rules for iM formation.

中文翻译：

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富含胞嘧啶的人类端粒DNA片段的i-Motif包含天然碱基病变

i-Motif（iM）是由富含胞嘧啶的序列形成的四链DNA结构，富含胞嘧啶的序列通常存在于基因组的功能重要部分中，例如基因和端粒的启动子。使用电子圆二色性和紫外线吸收光谱法和电泳方法，我们检查了四种天然存在的DNA碱基损伤对人端粒DNA序列（C ₃ TAA）₃ C ₃形成的iM折叠和稳定性的影响。T.结果表明，TAA环损伤，嘌呤位点和8-氧代腺嘌呤替代腺嘌呤，5-羟甲基尿嘧啶替代胸腺嘧啶仅在一定程度上干扰了iM的形成。尿嘧啶的存在是由胞嘧啶的酶促或自发脱氨作用形成的，它使iM的形成移向更酸性的pH值，同时明显降低了iM的稳定性。该效果取决于序列中损坏部位的位置。结果使我们能够制定其他有关iM形成的规则。