DNAの八重らせん構造およびその開裂四重鎖構造とそれらの生物学的意義

抄録

Recent human genome projects have revealed that exons encoding proteins count only a few percents, whereas many kinds of repetitive sequences occupy more than 50 % of genome. Some of the latter are related to genetic diseases, but their biological functions and structures are still unknown. Two X-ray structures of a short DNA fragment of d (gcGA [G] ₁Agc) show that four base-intercalated duplexes are assembled to form an octaplex at a low K⁺ concentration, in which the eight G₅ residues form a stacked double G-quartet in the central part. At a higher K⁺ concentration, however, the octaplex is split into just two halves. These structural features suggest a folding process according to a double Greek-key motif for eight tandem repeats of d (ccGA [G] ₄Agg) found in Variable number of tandem repeat (VNTR) immediately adjacent to the human pseudoautosomal telomere. Such a packaging of the repeats could facilitate slippage of a certain VNTR sequence during DNA replication, to induce length polymorphism by increasing or decreasing of the repeats.