7S particles from Xenopus oocytes were completely dissociated under non-reducing conditions. Studies using glycerol gradient centrifugation show that unlike the native 7S particle in which 5S RNA and TFIIIA co-sedimented in a fairly sharp peak, the RNA from the denatured 7S sedimented at the position corresponding to the 5S RNA and the TFIIIA sedimented as a wide peak between 6S and 12S. Thioredoxin from E.coli can catalyze the reactivation of the TFIIIA as measured by its ability to reform the 7S particle. The rate of reactivation with thioredoxin was significantly greater than with dithiothreitol. Oxidized thioredoxin was unable to reactivate TFIIIA. Pure TFIIIA can be inactivated and subsequently reactivated in the same way by formation of a cross-linked structure via intermolecular disulfide bridges.
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