Red Ice Creations: Unusual nucleic-acid structure may have role in regulating some genes. There is no more iconic image in biology than that of DNA’s double-stranded helix, which coils and supercoils on itself to form dense chromosomes. But a quite different, square-shaped type of DNA structure can easily be created in the laboratory by the folding of synthetic DNA strands rich in guanine, one of the building blocks of DNA. Scientists have long believed that these so-called ’G-quadruplex structures’ may occasionally form in the DNA of living cells. A G-quadruplex comprises four guanines from different places along a G-rich strand held together by a special type of hydrogen bonding to form a compact square structure that interrupts the DNA helix
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