DNA rearrangements in Euplotes crassus coincide with discrete periods of DNA replication during the polytene chromosome stage of macronuclear development.
Macronuclear development in Euplotes crassus begins with polytenization of micronuclear chromosomes and is accompanied by highly precise excision of DNA sequences known as internal eliminated sequences and transposon-like elements (Tecs). Quantitation of radiolabeled-precursor incorporation 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 periods even at a single locus. We also show that Tec and internal eliminated sequence excisions are coincident in the second replication period, thus providing further evidence for similarity in their excision mechanism. Inhibition of DNA synthesis with hydroxyurea diminishes Tec element excision, indicating that replication is an important aspect of the excision process.
Department of Cell and Molecular Biology, Northwestern University Medical School, Chicago, Illinois 60611, USA.
J S
JS
Frels
C L
CL
Jahn
D000818:Animals; D001483:Base Sequence; D002875:Chromosomes / Q000502:physiology*; D003433:Crosses, Genetic; D004261:DNA Replication / Q000187:drug effects; D004251:DNA Transposable Elements; D016054:DNA, Protozoan / Q000096:biosynthesis* / Q000235:genetics*; D016812:Euplotes / Q000235:genetics / Q000254:growth & development*; D006918:Hydroxyurea / Q000494:pharmacology; D016133:Polymerase Chain Reaction; D013045:Species Specificity; D013936:Thymidine / Q000378:metabolism; D013942:Thymine Nucleotides / Q000378:metabolism
D004251:DNA Transposable Elements; D016054:DNA, Protozoan; D013942:Thymine Nucleotides; C024157:thymidine 5'-triphosphate; D013936:Thymidine; D006918:Hydroxyurea