Regulators of gene expression physically interact with their targets. (A) Transcriptional regulation. Regulatory TFs function by binding to proteins and to DNA. Black boxes, exons; blue squares, cis-regulatory DNA elements; red ellipses, TFs; arrow, transcription start site. Curved arrows indicate activation of gene expression and blunt “arrow” indicates transcriptional repression. AD, transcription activation domain; RD, transcription repression domain; DB, DNA binding domain. (B) Post-transcriptional regulation. RNA binding proteins and microRNAs function by directly interacting with their target mRNAs. Arrow, transcription start site; purple box, microRNA gene; green line, 3′ UTR of target microRNA (purple line); yellow circle, RNA binding protein. Upstream regulation of miRNA expression (by the pink TF binding to the light blue element) is indicated and connects transcriptional and post-transcriptional gene regulation.
