Abstract
We report that TFIIIA, the positive transcription factor of the 5S RNA gene, induces DNA gyration in Xenopus oocyte extracts. The reaction uses one molecule of TFIIIA per molecule of DNA and is highly specific for 5S DNA plasmids. DNA gyration also requires the oocyte supernatant, ATP, and Mg2+, and is inhibited by novobiocin, suggesting that it is catalyzed by a type II DNA topoisomerase. The chromatin assembled with TFIIIA is dynamic and rapidly relaxed by novobiocin; the chromatin assembled without TFIIIA is static and unaffected by novobiocin. The torsionally strained DNA is produced in a novel concerted reaction: all of the 5S DNA molecules gyrate at TFIIIA-5S DNA ratios equal to or above 1, and none of them gyrate at TFIIIA-5S DNA ratios below 1. We discuss the biological implications of this eukaryotic DNA gyration.
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