The two activation domains of the Brn-3a transcription factor have distinct functional properties

The Brn-3a transcription factor has two distinct activation domains located, respectively, at the N-terminus and the C-terminus (coincident with the DNA binding POU domain) which differ in their effects on different target promoters, To analyze whether these regions could function when Linked to a heterologous DNA binding domain, they were each linked to the GAL4 DNA binding domain. Here we show that the N-terminal domain constitutes a discrete activation domain which can function when linked to a heterologous DNA binding domain. Under these conditions this domain can activate at different distances upstream of the transcriptional start site but does not do so when bound downstream of the start site, In contrast, the POU activation domain cannot activate transcription when delivered to DNA via a heterologous DNA binding domain, but can function when Linked to such a domain if bound to DNA via its own appropriate binding site, The reasons for this difference between these two domains are discussed in terms of the ability of the POU domain to bind to single stranded DNA and serve as a site for protein-protein interactions (C) 1997 Elsevier Science Ltd. All rights reserved.