DNA REARRANGEMENTS IN EUPLOTES-CRASSUS COINCIDE WITH DISCRETE PERIODSOF DNA-REPLICATION DURING THE POLYTENE CHROMOSOME STAGE OF MACRONUCLEAR DEVELOPMENT

Macronuclear development in Euplotes crassus begins with polytenizatio n of micronuclear chromosomes and is accompanied by highly precise exc ision of DNA sequences known as internal eliminated sequences and tran sposon-like elements (Tecs). Quantitation of radiolabeled-precursor in corporation into DNA indicates that DNA synthesis during formation of polytene chromosomes is not continuous and occurs during two distinct periods. We demonstrate that the timing of Tec excision coincides with these replication periods and that excision can occur during both per iods even at a single locus. Wi: also show that Tec and internal elimi nated sequence excisions are coincident in the second replication peri od, thus providing further evidence for similarity in their excision m echanism. Inhibition of DNA synthesis with hydroxyurea diminishes Tec element excision, indicating that replication is an important aspect o f the excision process.