The transcriptional activator protein Bas2 is required to express more than 20 genes in pathways for purine nucleotide and histidine biosynthesis, phosphate utilization, and the HO endonuclease by acting with co-regulator proteins Bas1, Pho4, and Swi5. The role that Bas2 plays in transcriptional activation may be to unmask latent activation domains in the co-regulator and to promote ternary complex formation between Bas2, the co-regulator, and DNA. We show that Bas2 also contributes to transcriptional activation by providing an activation domain. We localize this domain in Bas2 to the C-terminal 156 amino acids using deletion analysis and fusion to a heterologous DNA binding domain. Additionally, we show that Bas2 makes direct contacts with Bas1. This interaction is detected by co-immunoprecipitation and by two-hybrid analysis. We localize the interaction region to the central portion of Bas2, from amino acids 112 to 404.