THE ABILITY OF THE INHIBITORY DOMAIN OF THE POU FAMILY TRANSCRIPTION FACTOR OCT-2 TO INTERFERE WITH PROMOTER ACTIVATION BY DIFFERENT CLASSES OF ACTIVATION DOMAINS IS DEPENDENT UPON THE NATURE OF THE BASAL PROMOTER ELEMENTS

The Oct-2 transcription factor contains an inhibitory domain which is able to repress transcription following DNA binding, Here we show that within the neuronally expressed Oct-2.5 form, the inhibitory domain c an strongly inhibit activation by transcription factor activation doma ins which are either composed predominantly of acidic residues or cont ain the HOB motif, whereas it has a weaker effect or no effect on prol ine-rich activation domains and on a glutamine rich domain, In contras t, the isolated inhibitory domain of Oct-2 can efficiently repress all types of activation domains, This effect is observed however, only on TATA box containing promoters and not on promoters containing an init iator motif. This widespread inhibition of different activation domain s and its dependence on the nature of the basal promoter elements indi cate that the inhibitory domain is likely to act by contacting a commo n downstream target of activation domains within the basal transcripti onal complex bound at the TATA box rather than quenching specific acti vation domains by direct interaction, These effects are discussed in t erms of the functional role of the inhibitory domain within Oct-2.5 an d the mechanism by which it acts.