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Molecular and Cellular Biology, November 2001, p. 7826-7838, Vol. 21, No. 22
Department of Biological Chemistry,
University of California, Irvine, California 92697
Received 15 June 2001/Returned for modification 19 July
2001/Accepted 9 August 2001
Retroviruses in nondividing cells and yeast retrotransposons must
transit the nuclear membrane in order for integration to occur.
Mutations in a bipartite basic motif in the carboxyl-terminal domain of
the Ty3 integrase (IN) protein were previously shown to block
transposition at a step subsequent to 3'-end processing of Ty3
extrachromosomal DNA. In this work, the Ty3 IN was shown to be
sufficient to target green fluorescent protein to the nucleolus. Mutations in the bipartite basic motif abrogated this localization. The
region containing the motif was shown to be sufficient for nuclear but
not subnuclear localization of a heterologous protein. Viruslike
particles (VLPs) from cells expressing a Ty3 element defective for
nuclear localization were inactive in an in vitro integration assay,
suggesting that nuclear entry is required to form active VLPs or that
this motif is required for post-nuclear entry steps. Ty3 inserts at
transcription initiation sites of genomic tRNA genes and plasmid-borne
5S and U6 RNA genes transcribed by RNA polymerase III. In situ
hybridization with Ty3- and Ty3 long terminal repeat-specific probes
showed that these elements which are associated with tRNA genes do not
colocalize with the ribosomal DNA (rDNA). However, a PCR assay of cells
undergoing transposition showed that Ty3 insertion does occur into the
5S genes, which, in yeast, are interspersed with the rDNA and
therefore, like Ty3 IN, associated with the nucleolus.
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.22.7826-7838.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Integrase Mediates Nuclear Localization of
Ty3
*
Corresponding author. Mailing address: Department of
Biological Chemistry, College of Medicine, University of California, Irvine, Irvine, CA 92697-1700. Phone: (949) 824-7571. Fax: (949) 824-2688. E-mail: sbsandme{at}uci.edu.
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