page_title: Post-transcriptional regulation
section_title: Significance
hierarchical_section_title: Post-transcriptional regulation / Significance
context_page_description: Post-transcriptional regulation is the control of gene expression at the RNA level, therefore between the transcription and the translation of the gene. It contributes substantially to gene expression regulation across human tissues.
context_section_description: This area of study has recently gained more importance due to the increasing evidence that post-transcriptional regulation plays a larger role than previously expected. Even though protein with DNA binding domains are more abundant than protein with RNA binding domains, a recent study by Cheadle et al. (2005) showed that during T-cell activation 55% of significant changes at the steady-state level had no corresponding changes at the transcriptional level, meaning they were a result of stability regulation alone.
  Furthermore, RNA found in the nucleus is more complex than that found in the cytoplasm:  more than 95% (bases) of the RNA synthesized by RNA polymerase II never reaches the cytoplasm. The main reason for this is due to the removal of introns which account for 80% of the total bases. Some studies have shown that even after processing the levels of mRNA between the cytoplasm and the nucleus differ greatly.
  Developmental biology is a good source of models of regulation, but due to the technical difficulties it was easier to determine the transcription factor cascades than regulation at the RNA level. In fact several key genes such as nanos are known to bind RNA but often their targets are unknown. Although RNA binding proteins may regulate post transcriptionally large amount of the transcriptome, the targeting of a single gene is of interest to the scientific community for medical reasons, this is RNA interference and microRNAs which are both examples of posttranscriptional regulation, which regulate the destruction of RNA and change the chromatin structure. To study post-transcriptional regulation several techniques are used, such as RIP-Chip (RNA immunoprecipitation on chip).
caption: A prokaryotic example: Salmonella enterica (a pathogenic γ-proteobacterium) can express two alternative porins depending on the external environment (gut or murky water), this system involves EnvZ (osomotic sensor) which activates OmpR (transcription factor) which can bind to a high affinity promoter even at low concentrations and the low affinity promoter only at high concentrations (by definition): when the concentration of this transcription factor is high it activates OmpC and micF and inhibits OmpF, OmpF is further inhibited post-transcriptionally by micF RNA which binds to the OmpF transcript[11]