<Li> mRNA Stability can be manipulated in order to control its half - life, and the poly (A) tail has some effect on this stability, as previously stated . Stable mRNA can have a half life of up to a day or more which allows for the production of more protein product; unstable mRNA is used in regulation that must occur quickly . </Li> <P> MicroRNAs (miRNAs) appear to regulate the expression of more than 60% of protein coding genes of the human genome . If an miRNA is abundant it can behave as a "switch", turning some genes on or off . However, altered expression of many miRNAs only leads to a modest 1.5 - to 4-fold change in protein expression of their target genes . Individual miRNAs often repress several hundred target genes . Repression usually occurs either through translational silencing of the mRNA or through degradation of the mRNA, via complementary binding, mostly to specific sequences in the 3' untranslated region of the target gene's mRNA . The mechanism of translational silencing or degradation of mRNA is implemented through the RNA - induced silencing complex (RISC). </P> <P> In metazoans and bacteria, many genes involved in post-post transcriptional regulation are regulated post transcriptionally . For Drosophila RBPs associated with splicing or nonsense mediated decay, analyses of protein - protein and protein - RNA interaction profiles have revealed ubiquitous interactions with RNA and protein products of the same gene . It remains unclear whether these observations are driven by ribosome proximal or ribosome mediated contacts, or if some protein complexes, particularly RNPs, undergo co-translational assembly . </P> <P> 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 . </P>

Post-transcription controls for the regulation of eukaryotic gene expression