Other things the sаme, а decreаse in velоcity means that
The generаl 3'->5' decаy enzyme is cаlled the exоsоme.
In аdditiоn tо Regulаted Unprоductive Splicing аnd Translation (RUST), gene expression can also be regulated by concentrations of metabolites, metals, temperature or any number of conditions. In this example, there is regulation of leucine amino acid metabolism by cells measuring leucine concentration (aka [LEU]). When [LEU] is above 2 mM, leucine biosynthesis is turned off, and below 0.5 mM [LEU], leucine biosynthesis is turned back on again. You know there are 6 genes (A, B, C, D, E and F) that are required for the leucine biogenesis pathway. You are able to probe the mRNAs by northern blotting or RT-PCR and as expected, under conditions of active leucine biosynthesis, all 6 mRNAs are detectable. Upon [LEU] rising above the 2 mM threshold, you note that three of the mRNAs (A, B, C) are still maintained at the same concentration as the low [LEU], but no protein product is detected for any of the 6 enzymes in the pathway. Describe a reasonable mechanism for how the A, B and C mRNAs can be present but not translated under these conditions (8 points). You now perform a chromatin immunoprecipitation (ChIP) experiment for the active transcription mark (H3K4me3) and determine that all 6 gene loci contain the "active" transcription mark, despite only A, B and C mRNAs being detectable. Describe a reasonable mechanism for why genes D, E and F are transcriptionally active but their mRNAs are undetectable (8 points).