| First Author | Kurtzman AL | Year | 2001 |
| Journal | Proc Natl Acad Sci U S A | Volume | 98 |
| Issue | 10 | Pages | 5602-7 |
| PubMed ID | 11331779 | Mgi Jnum | J:69407 |
| Mgi Id | MGI:1934538 | Doi | 10.1073/pnas.101129698 |
| Citation | Kurtzman AL, et al. (2001) Ubc9 interacts with a nuclear localization signal and mediates nuclear localization of the paired-like homeobox protein Vsx-1 independent of SUMO-1 modification. Proc Natl Acad Sci U S A 98(10):5602-7 |
| abstractText | Vsx-1 is a paired-like:CVC homeobox gene whose expression is linked to bipolar cell differentiation during zebrafish retinogenesis. We used a yeast two-hybrid screen to identify proteins interacting with Vsx-1 and isolated Ubc9, an enzyme that conjugates the small ubiquitin-like modifier SUMO-1. Despite its interaction with Ubc9, we show that Vsx-1 is not a substrate for SUMO-1 in COS-7 cells or in vitro. When a yeast two-hybrid assay is used, deletion analysis of the interacting domain on Vsx-1 shows that Ubc9 binds to a nuclear localization signal (NLS) at the NH(2) terminus of the homeodomain. In SW13 cells, Vsx-1 localizes to the nucleus and is excluded from nucleoli. Deletion of the NLS disrupts this nuclear localization, resulting in a diffuse cytoplasmic distribution of Vsx-1. In SW13 AK1 cells that express low levels of endogenous Ubc9, Vsx-1 accumulates in a perinuclear ring and colocalizes with an endoplasmic reticulum marker. However, NLS-tagged STAT1 protein exhibits normal nuclear localization in both SW13 and SW13 AK1 cells, suggesting that nuclear import is not globally disrupted. Cotransfection of Vsx-1 with Ubc9 restores Vsx-1 nuclear localization in SW3 AK1 cells and demonstrates that Ubc9 is required for the nuclear localization of Vsx-1. Ubc9 continues to restore nuclear localization even after a C93S active site mutation has eliminated its SUMO-1-conjugating ability. These results suggest that Ubc9 mediates the nuclear localization of Vsx-1, and possibly other proteins, through a nonenzymatic mechanism that is independent of SUMO-1 conjugation. |
