Transactivation in a geminivirus: AL2 gene product is needed for coat protein expression.

The beta-glucuronidase (GUS) reporter gene was used to replace the coat protein gene (open reading frame AR1) of tomato golden mosaic virus (TGMV) and transiently expressed in tobacco protoplasts. While these TGMV/GUS genomes gave a high level of GUS activity, genomes which also contained a mutation in the AL2 open reading frame (TGMV/GUS/AL2-) did not express GUS. GUS activity could be restored by cotransfecting protoplasts with the TGMV/GUS/AL2- genome and a wild-type TGMV genome. Thus, the AL2 gene product transactivates expression of TGMV coat protein gene.