Chat with AIExam 9: Post-Transcriptional Gene Control
The tissue-specific expression of antisense RNA is one experimental approach for selectively shutting down production of a protein.For example,some researchers have proposed that this approach could be used to regulate the production of pollen in tobacco,oilseed rape,and maize.The controlled production of sterile male plants,for example,would eliminate the problem of self-fertilization in the production of hybrid maize seeds.In this approach,expression of antisense RNA would be controlled by coupling it to a promoter that is specific to anthers,the part of flowers where pollen is produced.Alternatively,the RNase activity inherent in self-splicing RNA might provide a sequence-specific means to regulate pollen production.Discuss how a catalytic RNA (i.e. ,a ribozyme)might be designed to prevent the expression of proteins needed for pollen production.
(38) 
VerifiedSome RNAs are capable of both sequence-specific base pairing and catalytic activity as an RNase.For example,when the 400-nucleotide-long intron sequence from Tetrahymena rRNA,a group I self-splicing RNA,is synthesized in a test tube,it folds and can bind two substrates,a guanine nucleotide and a substrate RNA chain.This synthetic intron then catalyzes the covalent attachment of the G to the substrate RNA,thereby cleaving the substrate RNA at a specific site.The release of the two RNA fragments frees the catalytic RNA for repeated rounds of catalysis.In principle,through the inclusion of the appropriate sequence for base pairing,a catalytic RNA can be designed that will bind to any substrate RNA and sever it at a specific site.Engineering a DNA sequence encoding a properly designed catalytic RNA under control of a tissue-specific set of promoter/enhancer elements and incorporating it into the germ line of plants could result in the tissue-specific synthesis of a ribozyme capable of selectively destroying a differentiation-specific mRNA required for pollen production.
Which of the following does not require enzymes?
(31) VerifiedB
The oocytes of multicellular animals contain stored mRNAs that encode numerous proteins required for early embryonic development.These proteins,however,are not translated until after fertilization and,therefore,a mechanism must be in place to ensure the stored mRNAs remain intact and untranslated before they are needed.Discuss the mechanism that keeps these stored mRNAs from being translated in the oocyte.
(39) VerifiedStored mRNAs in oocytes have short poly(A)tails,consisting of ~20-40 residues.These short tails can bind only a few molecules of cytoplasmic poly(A)-binding protein (PABPI),which is not enough to interact with the initiation factor eIF4G.Following fertilization,the poly(A)tail increases in length with the addition of ≈150 A residues.This facilitates the binding of several PABPI molecules,allowing them to interact with eIF4G in a multimeric complex with eIF4E,other initiation factors,and the cap at the 5´ end of the mRNA.The stable conformation that forms is required for the initiation of translation.Thus,stored mRNAs are not translated efficiently because their short poly(A)tails do not provide enough binding sites to allow PABPI to implement the stability the complex requires for translation initiation.
The spliceosomal splicing cycle involves ordered interactions among a pre-mRNA and several U snRNPs.According to the current model of spliceosomal splicing,which intermediate(s)in the splicing of a pre-mRNA containing one intron should be immunoprecipitated by anti-U2 snRNP? Which additional intermediate(s)should be immunoprecipitated by anti-U2AF?
(28) In birds,a gene encoding a Ca²⁺-activated K⁺ channel is expressed in auditory hair cells as multiple mRNAs,which encode for proteins that open at different Ca²⁺ concentrations.The Ca²⁺ concentration at which the channel opens allows these cells to respond to different sound frequencies.Which one of the following would explain the appearance of the various isoforms of this particular channel?
(38) Sequencing of small RNAs isolated from metazoan cells revealed low levels of short,capped
RNAs transcribed from both the sense and antisense strands of DNA.What is the term used to describe the fact that the majority of the metazoan genome is transcribed?
(27) The cell contains numerous organelles,all with specific functions,but the one that plays a key role in the digestion of ribosomes,mitochondria,and other organelles is the:
(31) The mammalian target of rapamycin (mTOR)complex 1 plays an integral role in all but one of these processes.Which one is mTOR not directly involved in?
(33) The finding that the short consensus sequence at the 5´ end of introns is complementary to a sequence near the 5´ end of U1 snRNA suggested that this snRNA must interact with pre-mRNA for splicing to occur.Describe three types of experimental evidence that indicate U1 snRNA is required for splicing.
(31) Some _____ have evolved a constitutive transport element within their genome,which allows for the export of unspliced RNAs into the cytoplasm.
(35) The export of mRNAs outside the nucleus requires several proteins that are post-translationally modified by:
(30) Knocking out the dicer gene in mammals would lead to a loss of:
(40) The branch-point A residue involved in lariat formation is part of the
(30) Indicate the order in which the following steps occur in the production of a mature mRNA.
(34) 
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