mRNA processing: AAUAAA sequence significance

Mature eukaryotic messenger RNAs are generated from larger precursors, the primary products of RNA polymerase II, by a series of processing steps, all of which take place in the cell nucleus. 3′-End processing is one of them. All pre-mRNAs in all eukaryotic organisms first lose sequences from their 3′-ends by an endonucleolytic cleavage. Almost all RNAs then receive a polyadenylate tail. The only known exceptions to this rule are the major histone mRNAs in metazoan cells. While they are also cleaved endonucleolytically, these RNAs are not polyadenylated, and the factors responsible for cleavage differ from the ones acting on all other pre-mRNAs. The poly(A) tails at the 3′-end of the mRNA function in the initiation of translation. A protein-mediated interaction with the cap at the 5′-end of the RNA helps to load the 40S ribosomal subunit onto the message. In addition, the poly(A) tails play a role in the regulation of mRNA stability as deadenylation is frequently the first and rate-limiting step of mRNA decay. Finally, the poly(A) tail is thought to be involved in the export of mRNA from the nucleus into the cytoplasm. Poly(A) tails are also found on prokaryotic mRNAs. However, whereas polyadenylation is an essential step in the production of functional mRNA in eukaryotes, it appears to be a prelude to degradation in bacteria (see elsewhere in this volume). Progress in the understanding of mRNA 3′-end formation has been summarized in numerous reviews. This overview will therefore be selective rather than comprehensive, focusing on recent advances in the biochemical understanding of the mechanism of cleavage and polyadenylation in mammalian cells and in Saccharomyces cerevisiae and on selected regulatory aspects. The basic 3′-end processing reaction is identical from yeast to man. However, the RNA sequences directing the process and the proteins catalyzing it are sufficiently distinct that the two systems will be discussed separately. Question: If the AAUAAA sequence is removed from a eukaryotic mRNA, which event will not occur? A) 5’ cap addition B) Cleavage and poly-adenylation of the mRNA C) Splicing of introns D) Transport to the cytoplasm E) None of the above #NikolaysGeneticsLessons #rnaProcessing #PolyATail #Polyadenylation #preMRNAProcessing #3EndProcessing #messangerRNAProcessing #mRNA #matureMRNA #preMRNA #precursorMRNA #eukaryotic #cellular #biology #RNAProcessingInEukaryotes #RNAProcessingInEukaryotesRNASplicing #cappingAndEditing #RNA #mrnaProcessing #rnaModifications #rnaSplicingAndProcessing #RnaSplicing #rnaEditing #rnaCapping #rnaProcessingInProkaryotes