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Mol. Cell. Biol., 10 1997, 6122-6130, Vol 17, No. 10
AW Johnson
XRN1 encodes an abundant cytoplasmic exoribonuclease, Xrn1p, responsible
for mRNA turnover in yeast. A screen for bypass suppressors of the
inviability of xrn1 ski2 double mutants identified dominant alleles of
RAT1, encoding an exoribonuclease homologous with Xrn1p. These RAT1 alleles
restored XRN1-like functions, including cytoplasmic RNA turnover, wild-type
sensitivity to the microtubule-destabilizing drug benomyl, and sporulation.
The mutations were localized to a region of the RAT1 gene encoding a
putative bipartite nuclear localization sequence (NLS). Fusions to green
fluorescent protein were used to demonstrate that wild-type Rat1p is
localized to the nucleus and that the mutant alleles result in
mislocalization of Rat1p to the cytoplasm. Conversely, targeting Xrn1p to
the nucleus by the addition of the simian virus 40 large-T-antigen NLS
resulted in complementation of the temperature sensitivity of a rat1-1
strain. These results indicate that Xrn1p and Rat1p are functionally
interchangeable exoribonucleases that function in and are restricted to the
cytoplasm and nucleus, respectively. It is likely that the higher
eukaryotic homologs of these proteins will function similarly in the
cytoplasm and nucleus.
Copyright © 1997, American Society for Microbiology
Rat1p and Xrn1p are functionally interchangeable exoribonucleases that are restricted to and required in the nucleus and cytoplasm, respectively
Department of Microbiology and Institute for Cellular and Molecular Biology, University of Texas at Austin, 78712-1095, USA. arlen@mail.utexas.edu
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