title: High fidelity developmental excision of Tec1 transposons and internal eliminated sequences in Euplotes crassus.
abstract: Following the sexual phase of its life cycle, the hypotrichous ciliate Euplotes crassus transforms a copy of its chromosomal micronucleus into a transcriptionally active macronucleus containing short, linear, gene-sized DNA molecules. Tens of thousands of DNA breakage and joining, or splicing, events occur during macronuclear development. The DNA removed by such events includes transposon-like elements, referred to as Tec1 elements, as well as segments of unique sequence DNA, termed internal eliminated sequences (IESs). Both types of elements are bounded by short direct repeats. In the current study, a polymerase chain reaction (PCR) and DNA sequencing strategy has been used to examine the fidelity of excision of two Tec1 elements and three IESs. In all cases, the vast majority of excision events were found to be precise, with one copy of the terminal direct repeats retained at the empty site in the macronuclear DNA molecule. These results, in combination with previous studies that have characterized the excised DNA elements, indicate that the two products of excision (the free element and the macronuclear DNA molecule) share DNA sequences. This suggests that excision events are initiated by staggered cuts in the chromosomal DNA.
authors.affiliation: Department of Biochemistry, University of Connecticut Health Center, Farmington 06030.
authors.forename: S L
authors.initials: SL
authors.lastname: Tausta
authors.forename: L R
authors.initials: LR
authors.lastname: Turner
authors.forename: L K
authors.initials: LK
authors.lastname: Buckley
authors.forename: L A
authors.initials: LA
authors.lastname: Klobutcher
mesh_terms: D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D002872:Chromosome Deletion; D016798:Ciliophora / Q000235:genetics*; D004251:DNA Transposable Elements; D016054:DNA, Protozoan / Q000235:genetics*; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D015183:Restriction Mapping
chemical_list: D004251:DNA Transposable Elements; D016054:DNA, Protozoan