The development of an entire organ can be triggered by a single regulatory protein. Regulatory proteins can be either activators or repressors of transcription. Controlling activity of regulatory proteins: protein synthesis; ligand binding; protein phosphorylation; addition of second subunit; unmasking. Regulatory genes are activated or inhibited by external signals (signal transduction). Synergy: the whole is greater than the sum of the individual parts. One gene activator protein results in 1 unit of transcription, while four gene activator proteins can result in 500 units of transcription. Combinatorial actions of regulatory proteins refer to how two proteins may bind to two binding sites, and then the activator or repressor binds those binding proteins.
How Are Patterns of Gene Expression Maintained?
|Feedback||Feedback mechanisms (negative/positive)|
|DNA Modification||DNA methylation -- chromatin compaction|
|Localization||localizing mRNAs to specific regions of the cytoplasm -- direct transport on cytoskeleton; random diffusion and trapping; generalized degradation in conjunction with localized protection|
|Translation||Proteins that bind to the 3' UTRs of mRNA can block translation (such as preventing polyA Binding Protein from binding to the adjacent polyA tail)|
|microRNA||Small noncoding RNAs. Approx 4% of mammalian genome. Complementary or partially complementary to 3' UTR sequences. Inhibit translation OR promote degradation of the target mRNA.|