how to identify significance of a protein interaction - (Dec/04/2007 )

hi all,
i think i should elaborate.

protein A is a repressor, protein B is a activator, they both interact
as a result the genes activated by protein B are repressed by A
now, the promoter regions of genes activated by B have no binding site for protein A,
so, just by interacting with protein B, protein A mediates its repressor activity.

thus, if now i want to find out a mutant of protein B that can still activate the genes activated by
the wild type protein B and cannot still interact with A, then there is a possibility that i might
be able to define the biological significance of this interaction.

what if i am unable to find such mutant, what other approach can i use

i am tired of thinking about this approach, any good suggestion???

syc06