Formation and properties of hairpin and tetraplex structures of guanine-rich regulatory sequences of muscle-specific genes

|Clustered guanine residues in DNA readily generate hairpin or a variety of tetrahelical structures. The myogenic determination protein MyoD was reported to bind to a tetrahelical structure of guanine-rich enhancer sequence of muscle creatine kinase (MCK) more tightly than to its target E-box motif [ K. Walsh and A. Gualberto ( 1992) J. Biol. Chem., 267, 13714-13718], suggesting that tetraplex structures of regulatory sequences of muscle-specific genes could contribute to transcriptional regulation. In the current study we show that promoter or enhancer sequences of various muscle-specific genes display a disproportionately high incidence of guanine clusters. The sequences derived from the guanine-rich promoter or enhancer regions of three muscle-specific genes, human sarcomeric mitochondrial creatine kinase (sMtCK), mouse MCK and alpha 7 integrin formed diverse secondary structures. The sMtCK sequence folded into a hairpin structure; the alpha 7 integrin oligonucleotide generated a unimolecular tetraplex; and sequences from all three genes associated to generate bimolecular tetraplexes. Furthermore, two neighboring non-contiguous guanine-rich tracts in the alpha 7 integrin promoter region also paired to form a tetraplex structure. We also show that homodimeric MyoD bound bimolecular tetraplex structures of musclespecific regulatory sequences more efficiently than its target E-box motif. These results are consistent with a role of tetrahelical structures of DNA in the regulation of muscle-specific gene expression.