DNA REARRANGEMENTS IN EUPLOTES-CRASSUS COINCIDE WITH DISCRETE PERIODSOF DNA-REPLICATION DURING THE POLYTENE CHROMOSOME STAGE OF MACRONUCLEAR DEVELOPMENT
Js. Frels et Cl. Jahn, DNA REARRANGEMENTS IN EUPLOTES-CRASSUS COINCIDE WITH DISCRETE PERIODSOF DNA-REPLICATION DURING THE POLYTENE CHROMOSOME STAGE OF MACRONUCLEAR DEVELOPMENT, Molecular and cellular biology, 15(12), 1995, pp. 6488-6495
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.