ABSTRACT
A similar example of protein-protein interactions regulating transcription factor activity, but in the opposite direction, is observed in the Fos and Jun proteins which regulate gene expression in response to phorbol ester treatment (Section 9.4). Thus, as noted in Section 8.2, the Fos protein cannot bind to DNA on its own but can do so only after forming a heterodimer with the Jun protein. This heterodimer then binds to DNA and activates transcription. Hence, in this case, the interaction with another protein allows Fos to activate transcription whereas in the case of the glucocorticoid receptor the interaction with hsp90 has the opposite effect.
