N. Sakamoto et al., Sticky DNA, a self-associated complex formed at long GAA center dot TTC repeats in intron 1 of the frataxin gene, inhibits transcriptions, J BIOL CHEM, 276(29), 2001, pp. 27171-27177
Friedreich's ataxia (FRDA) is an autosomal recessive neurodegenerative dise
ase caused by the expansion of GAA.TTC repeats in the first intron of the f
rataxin (X25) gene. FRDA patients carrying two expanded GAA.TTC repeats sho
w very low levels of mature frataxin mRNA and protein. A novel type of unus
ual DNA structure, sticky DNA, was previously found in the expanded GAA.TTC
repeats from FRDA patients, To evaluate the effect of sticky DNA on transc
ription, in vitro transcription studies of (GAA.TTC), repeats (where n = 9-
150) were carried out using T7 or SP6 RNA polymerase, When a gel-isolated s
ticky DNA template was transcribed, the amount of full-length RNA synthesiz
ed was significantly reduced compared with the transcription of the linear
template, Surprisingly, transcriptional inhibition was observed not only fo
r the sticky DNA template but also another DNA molecule used as an internal
control in an orientation-independent manner. The molecular mechanism of t
ranscriptional inhibition by sticky DNA was a sequestration of the RNA poly
merases by direct binding to the complex DNA structure. Moreover, plasmids
containing the (GAAGGA.TCCTTC)(65) repeat, which does not form sticky DNA,
did not inhibit in vitro transcription, as expected. These results suggest
that the role of sticky DNA in FRDA may be the sequestration of transcripti
on factors.