| Abstract: | When the topoisomerase II inhibitor, novobiocin, is administered to embryonic chicken red blood cells, it induces the in vivo release of an endogenous nuclease which cleaves specifically within internucleosomal spacer DNA and within nuclease-hypersensitive sites in the active chromatin of intact cells. This in vivo released nuclease activity is induced by novobiocin only in metabolically active immature red blood cells. Little induction occurs in mature erythrocytes and no induction occurs in cells previously treated with 2,4-dinitrophenol. Although novobiocin is required to induce release and/or activation of the nuclease, the activity of the nuclease, once activated, is independent of novobiocin. Analysis of the cleaved DNA in drug-treated immature cells demonstrates that the novobiocin-induced nuclease has an unusual blunt-ended double-stranded mode of cleavage. Because of its special properties and apparent chromatin related function in vivo, the novobiocin-induced nuclease activity offers a novel and useful in vivo and in vitro probe of chromatin structure. |
