Final answer:
Transcriptional activators work by enhancing RNA polymerase interaction with promoters, facilitated by intermediary proteins like bZIP.
Step-by-step explanation:
Transcriptional activators are proteins that enhance the interaction between RNA polymerase and a specific promoter, facilitating the initiation of transcription. An intermediary protein such as the bZIP protein can be an example of a transcription factor. It contains a basic region for binding DNA and a leucine zipper for dimerization, which is essential in the activation or repression of signal transduction pathways in plant defenses against pathogens.
Additionally, epigenetic modifications play a significant role in transcription regulation through chromatin remodeling. Histone modifications such as acetylation and methylation can unwind or condense chromatin structure, thereby regulating gene expression. For instance, histone acetylation by HAT enzymes tends to open the DNA for transcription, enhancing the recruitment of other proteins that further modify chromatin's conformation.