A nuclear localization sequence endows @entity1 XXXX with cytotoxic activity.

@entity1 @entity788 @entity137 @entity5 @entity534
Some members of the ribonuclease superfamily, such as Onconase, are cytotoxic to @entity5 cells. This is not the case for @entity1 @entity788 . This lack of @entity137 is probably a result of the inhibition exerted by the cytosolic ribonuclease inhibitor once the protein has reached the cytosol. Until now, all cytotoxic @entity1 @entity788 variants have been described as being resistant to the inhibitor. Here, we report on the characterization of a cytotoxic variant of @entity1 @entity788 which has an @entity534 triplet introduced onto one of its surface-exposed loops. Despite its sensitivity to the inhibitor, this variant, called PE5, was only 5-15 times less cytotoxic than Onconase. When it was taken up by cells, it was only observed within late compartments of the endocytic pathway, probably because the number of molecules transported to the cytosol was too small to allow their visualization. Nuclear import assays showed that the @entity534 triplet endows PE5 with a nuclear localization signal. In these experiments, PE5 was efficiently transported to the nucleus where it was initially localized in the nucleolus. Although the @entity534 introduction modified the net charge of the protein and somehow impaired recognition by the cytosolic inhibitor, control variants, which had the same number of charges or were not recognized by the inhibitor, were not toxic. We concluded that targeting a ribonuclease to the nucleus results in @entity137 . This effect is probably due to ribonuclease interference with rRNA processing and ribosome assembly within the nucleolus.
