Concluding Remarks

We have discussed a variety of mechanisms by which repressors/corepressors inhibit transcription. To activate transcription, it is essential that activators, bound to an enhancer located far from the core promoter, contact the preinitiation complex containing RNA polymerase II directly and/or indirectly through multiple coactivator complexes, such as the Mediator complex (Lemon and Tjian, 2000). In principle, disruption of these interactions at any level could lead to repression, so there might be more molecular mechanisms yet to be discovered. Some corepressors are known to interact with specific amino acid sequences (motifs or domains). For instance, dCtBP and Groucho interact with specific motifs, PxDLS and WRPW/FKPY/FxIxxIL, respectively. Specific amino acids of the DNA-binding factors/ coregulators can be modified, although the consensus sequences allowing such modifications are not often tight. A profound deeper knowledge of such "sequence features" will enable us to easily predict whether a factor of interest can work as an activator or a repressor.

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