Activity of DNA topoisomerase I and quiescence of embryo cells in seeds ofPisum sativumL.

Abstract
DNA topoisomerase activity is present at a very early stage of germination in nuclear extract of pea root meristems. The activity of this enzyme changes before the onset of replicative DNA synthesis, thus suggesting the existence of a correlation between DNA topoisomerase I and events taking place during the release of cells from a quiescent state. An antibody prepared against a human topoisomerase I is able to immuno-precipitate part of the DNA topoisomerase activity present in pea nuclear extracts, and recognizes a protein with a molecular weight of 45 kDa. We suggest that the 45 kDa protein is a DNA topoisomerase I; its presence during embryogenesis and its storage in dry seeds would explain the presence of DNA topoisomerase I activity during early stages of germination.
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