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Molecular and Cellular Biology, November 2000, p. 8390-8396, Vol. 20, No. 22
Department of Biochemistry, Purdue
University, West Lafayette, Indiana 47907
Received 12 June 2000/Returned for modification 14 July
2000/Accepted 11 August 2000
The micronuclear DNA of Paramecium tetraurelia is
estimated to contain over 50,000 short DNA elements that are precisely
removed during the formation of the transcriptionally active
macronucleus. Each internal eliminated sequence (IES) is bounded by
5'-TA-3' dinucleotide repeats, a feature common to some classes of DNA transposons. We have developed an in vivo assay to analyze these highly
efficient and precise DNA excision events. The microinjection of a
cloned IES into mating cells results in accurately spliced products,
and the transformed cells maintain the injected DNA as extrachromosomal
molecules. A series of deletions flanking one side of a 28-bp IES were
constructed and analyzed with the in vivo assay. Whereas 72 bp of DNA
flanking the eliminated region is sufficient for excision, lengths of
31 and 18 bp result in reduced excision and removal of all wild-type
sequences adjacent to the TA results in complete failure of excision.
In contrast, nucleotide mutations within the middle of the 28-bp IES do
not prevent excision. The results are consistent with a functional role
for perfect inverted repeats flanking the IES.
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Developmentally Regulated Excision of a 28-Base-Pair Sequence
from the Paramecium Genome Requires Flanking DNA
and
*
Corresponding author. Mailing address: Biochemistry
Building, Purdue University, West Lafayette, IN 47907. Phone: (765)
494-1632. Fax: (765) 494-7897. E-mail: forney{at}purdue.edu.
Paper number 16335 from the Purdue Agricultural Experiment Station.
Present address: California Institute of Technology, Pasadena, CA 91125.
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