The tomato golden mosaic virus transactivator (TrAP) is a single- stranded DNA and zinc-binding phosphoprotein with an acidic activation domain

Abstract

The AL2 gene found in members of the genus Begomovirus of the Geminiviridae encodes a transcriptional activator protein (TrAP; also known as AL2, AC2, or C2 protein). TrAP activates expression from the viral coat protein (CP) and BR1 movement gene promoters in mesophyll cells and protoplasts and acts to derepress the CP promoter in vascular tissue. The experiments presented here were designed to elucidate some of the biochemical properties of this multifunctional regulatory protein and to define its activation domain. The results indicate that TrAP from tomato golden mosaic virus (TGMV) binds single-stranded DNA in a sequence nonspecific manner and only weakly interacts with double-stranded DNA, confirming earlier results obtained with TrAP from other begomoviruses. In addition, evidence is presented that indicates that TrAP binds zinc and that zinc is necessary for optimal interaction with ssDNA. We also show that TrAP is phosphorylated when expressed in insect cells and that it contains a transcriptional activation domain of the acidic type. The minimal activation domain is quite small; the region comprising only the 15 C-terminal amino acids of the protein is capable of activating transcription in mouse fibroblasts (NIH3T3 cells) when fused to a heterologous DNA-binding domain.