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Molecular and Cellular Biology, January 1999, p. 484-494, Vol. 19, No. 1
Department of Zoology and Genetics, Iowa
State University, Ames, Iowa 50011
Received 27 April 1998/Returned for modification 16 June
1998/Accepted 19 October 1998
The yeast retrotransposon Ty5 preferentially integrates into
regions of silent chromatin. Ty5 cDNA also recombines with homologous sequences, generating tandem elements or elements that have exchanged markers between cDNA and substrate. In this study, we demonstrate that
Ty5 integration depends upon the conserved DD(35)E domain of integrase
and cis-acting sequences at the end of the long terminal repeat (LTR) implicated in integrase binding. cDNA recombination requires Rad52p, which is responsible for homologous recombination. Interestingly, Ty5 cDNA recombines at least three times more frequently with substrates in silent chromatin than with a control substrate at an
internal chromosomal locus. This preference depends upon the Ty5
targeting domain that is responsible for integration specificity, suggesting that localization of cDNA to silent chromatin results in the
enhanced recombination. Recombination with a telomeric substrate
occasionally generates highly reiterated Ty5 arrays, and mechanisms for
tandem element formation were explored by using a plasmid-based
recombination assay. Point mutations were introduced into plasmid
targets, and recombination products were characterized to determine
recombination initiation sites. Despite our previous observation of the
importance of the LTR in forming tandem elements, recombination cannot
simply be explained by crossover events between the LTRs of substrate
and cDNA. We propose an alternative model based on single-strand
annealing, where single-stranded cDNA initiates tandem element
formation and the LTR is required for strand displacement to form a
looped intermediate. Retrotransposons are increasingly found associated
with chromosome ends, and amplification of Ty5 by both integration and
recombination exemplifies how retroelements can contribute to telomere dynamics.
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
cDNA of the Yeast Retrotransposon Ty5
Preferentially Recombines with Substrates in Silent
Chromatin
*
Corresponding author. Mailing address: 2208 Molecular
Biology Building, Department of Zoology and Genetics, Iowa State
University, Ames, IA 50011. Phone: (515) 294-1963. Fax: (515) 294-6755. E-mail: voytas{at}iastate.edu.
This is journal paper J-17884 of the Iowa Agriculture and Home
Economics Experiment Station, Ames, Iowa, project 3383.
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