Rat1p and Xrn1p are functionally interchangeable exoribonucleases that are restricted to and required in the nucleus and cytoplasm, respectively

These results indicate that Xrn1p and Rat1p are functionally interchangeable exoribonucleases that function in and are restricted to the cytoplasm and nucleus, respectively

A W Johnson


Scholarcy highlights

  • In the yeast Saccharomyces cerevisiae, the 5Ј33Ј exoribonuclease I, Xrn1p, encoded by the XRN1 gene, is the primary cytoplasmic RNase responsible for mRNA degradation
  • In separate experiments, targeting Xrn1p to the nucleus rescued rat1-1 mutants. These results provide compelling evidence that Rat1p and Xrn1p are functionally equivalent proteins localized to the nucleus and cytoplasm, respectively, and that the essential role of RAT1 is in the nucleus
  • Since the nuclear localization sequence⌬ mutant complemented the rat1-1 allele, either Rat1p can carry out its essential role in the cytoplasm in a capacity that Xrn1p cannot, or sufficient Rat1p still enters the nucleus for nuclear activity, suggesting that the protein may bear an additional NLS or can enter the nucleus by another mechanism
  • Since wild-type Xrn1p is cytoplasmic and does not complement rat1-1, even when XRN1 is present on a high-copy-number plasmid, these results show that the simian virus 40 large-T-antigen NLS is sufficient to direct Xrn1p to the nucleus
  • The finding that suppressors of xrn1 ski2 lethality were mutations in a putative NLS of Rat1p suggested that suppression was the result of mislocalization of Rat1p to the cytoplasm, where it could substitute for Xrn1p
  • It is likely that within this family of eukaryotic exoribonucleases, the Xrn1 subfamily exists in the cytoplasm, where these proteins are responsible for mRNA turnover, whereas the proteins of the Rat1 subfamily are in the nucleus, where they function in some as yet unknown but essential role in RNA degradation

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