Sumoylation of Rta of Epstein-Barr virus is preferentially enhanced by PIASxβ

Epstein-Barr virus (EBV) expresses an immediate-early protein, Rta, to activate the viral lytic cycle. This study identifies PlASx alpha and PIASx beta as binding partners of Rta in a yeast two-hybrid screen and demonstrates the binding of Rta to PIASx alpha and PIASx beta in vitro by GST pull-down analysis. Coimmunoprecipitation experiments and- indirect immunofluorescence analysis show that Rta interacts and colocalizes with PIASx alpha and PIASx beta in the nucleus. These interactions seem to enhance Rta sumoylation as transfecting plasmids expressing PIASxa, PIASx beta, Ubc9, or SUMO-1 increase the capacity of Rta to transactivate a promoter that contains an Rta-response element and the promoters of p21 and BNLF I in transient transfection assay. This study also finds that Rta sumoylation is preferentially enhanced by PIASx beta, which could be attributed to the fact that PIASx beta, compared to PIASx alpha, has a strong affinity to Rta, suggesting that affinity of a SUMO E3 ligase to its target protein influences the function of protein surnoylation. (c) 2006 Elsevier B.V. All rights reserved.