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Gradual and oriented B-Z transition in 5'-untranscribed region of mouse ribosomal DNA.

1994; Elsevier BV; Volume: 269; Issue: 30 Linguagem: Inglês

10.1016/s0021-9258(17)32158-0

1083-351X

Annie-Claude Albert, A.M. Roman, Gérard Bouche, M. Leng, A. Rachid Rahmouni,

Genomics and Chromatin Dynamics

The structural transition of an alternating purine-pyrimidine sequence (CG)5(TG)28) from the 5'-untranscribed region of the mouse ribosomal DNA was analyzed by two-dimensional gel electrophoresis and chemical probes. The repeat undergoes a supercoil-dependent gradual and oriented B-Z transition. At a threshold level of negative supercoiling, a limited region of the repeat encompassing the (CG)5 motif converts cooperatively into Z-DNA. As the superhelical stress increases, the Z-structure propagates along the remaining part of the repeat by successive transitions until the full-length sequence is converted. By in situ OsO4 probing experiments, we show also that this (TG)n-containing repeat adopts the Z-structure in Escherichia coli.