Details

Autor(en) / Beteiligte

• Greaves, David R.
• Patient, Roger K.
• Lilley, David M.J.

Titel

Facile cruciform formation by an (A-T) 34 sequence from a Xenopus globin gene

Ist Teil von

• Journal of molecular biology, 1985-10, Vol.185 (3), p.461-478

Ort / Verlag

Oxford: Elsevier Ltd

Erscheinungsjahr

1985

Link zum Volltext

Quelle

Elsevier Journal Backfiles on ScienceDirect (DFG Nationallizenzen)

Beschreibungen/Notizen

• We have studied the structure adopted by an (A-T) 34 sequence from a Xenopus globin gene when present in a negatively supercoiled plasmid. A variety of enzyme and chemical probing experiments and electrophoretic migration shift methods reveal that the sequence adopts cruciform geometry at moderate levels of supercoiling. The structure has the lowest free energy of formation yet observed for a cruciform, and no detectable kinetic barrier preventing rapid interconversion between extruded and unextruded conformations. Analysis of band-shift experiments reveals a twist change on cruciform formation of −5.8, slightly smaller than the −6.5 we would predict on the basis of a transition from B DNA. An attractive explanation consistent with this discrepancy is that the (A-T) 34 stretch is locally underwound to about 11.7 base-pairs/helical turn at low levels of supercoiling. This calculation is made on the assumption that the cruciform junction is structurally similar to those examined previously, which is supported by the nuclease digestion results. This perturbed helical structure could be of considerable biological significance.