Js. Frels et al., DIFFERENTIAL REPLICATION AND DNA ELIMINATION IN THE POLYTENE CHROMOSOMES OF EUPLOTES-CRASSUS, Molecular biology of the cell, 7(5), 1996, pp. 755-768
The transposon-like Tec elements of Euplotes crassus are precisely exc
ised during formation of polytene chromosomes in the developing macron
ucleus. To determine whether all Tec elements exhibit identical develo
pmental timing of excision, we used polymerase chain reaction to visua
lize amplification and diminution at numerous randomly selected Tec in
sertion sites. Two classes of sites are evident. Early replicating sit
es show one or more rounds of amplification and diminution (correspond
ing to excision) and frequently occur within macronuclear-destined seq
uences. Late replicating sites do not undergo diminution until chromos
ome fragmentation and are predominantly associated with eliminated seq
uences, We conclude that the previously described clustering of macron
uclear-destined sequences in the micronuclear genome allows for their
differential replication at the polytene stage and results in targetin
g of these sequences for transcriptional activation and highly specifi
c deletion and chromosome fragmentation processes.