Abstract:
:The existence of torsional stress in eukaryotic chromatin has been controversial. To determine whether it could be detected, we probed the structure of an alternating AT tract. These sequences adopt cruciform geometry when the DNA helix is torsionally strained by negative supercoiling. The single-strand-specific nuclease P1 was used to determine the structure of an alternating AT sequence upstream of the Xenopus beta-globin gene when assembled into chromatin in microinjected Xenopus oocytes. The pattern of cleavage by P1 nuclease strongly suggests that the DNA in this chromatin template is under torsional stress. The cruciform was detected specifically in the most fully reconstituted templates at later stages of chromatin assembly, suggesting that negative supercoiling is associated with chromatin maturation. Furthermore, the number of torsionally strained templates increased dramatically at the time when transcription of assembled chromatin templates began. Transcription itself has been shown to induce supercoiling, but the requisite negative supercoiling for cruciform extrusion by (AT)n in oocytes was not generated in this way since the characteristic P1 cutting pattern was retained even when RNA polymerase elongation was blocked with alpha-amanitin. Thus, torsional stress is associated with transcriptional activation of chromatin templates in the absence of ongoing transcription.
journal_name
Mol Cell Bioljournal_title
Molecular and cellular biologyauthors
Leonard MW,Patient RKdoi
10.1128/mcb.11.12.6128subject
Has Abstractpub_date
1991-12-01 00:00:00pages
6128-38issue
12eissn
0270-7306issn
1098-5549journal_volume
11pub_type
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