Section 6
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What are the roles of small nuclear RNAs (snRNAs) in rRNA processing?
• Sites of snRNP assembly and storage: Cajal bodies and nuclear speckles • Function in pre-rRNA processing • Involved in pre-rRNA cleavage, ribose methylation, and pseudouridylation Nucleoli contain over 300 proteins and about 200 snoRNAs that assist in these processes.
What is the function of small nucleolar RNAs (snoRNAs)?
Function in pre-rRNA processing SnoRNAs are localized to the nucleolus and are essential for pre-rRNA cleavage, ribose methylation, and pseudouridylation.
What is the significance of the nucleolus in ribosome formation?
• Assembly of ribosomal precursor RNAs with ribosomal proteins • Transport of ribosomal proteins from cytoplasm to nucleolus • Formation of pre-ribosomal particles The final stages of ribosomal subunit maturation occur after the export of pre-ribosomal particles to the cytoplasm.
How are mRNAs exported from the nucleus?
• Distinct mechanism independent of Ran • Involves a set of at least 20 proteins • Associated with an mRNA exporter complex The exporter complex is recruited to pre-mRNAs during splicing and polyadenylation.
True or false: tRNAs and miRNAs are exported from the nucleus by the same mechanism as mRNAs.
FALSE tRNAs and miRNAs are exported by specific exportins, while mRNAs use a distinct mechanism.
What regulates the nuclear import of transcription factors?
• Association with cytoplasmic proteins that mask nuclear localization signals • Direct phosphorylation of transcription factors This regulation is crucial for controlling gene expression.
What happens to NF-κB in the absence of extracellular signals?
It remains in an inactive complex with IκB, which masks its nuclear localization signal This prevents NF-κB from being transported to the nucleus.
What is the role of Xist in X chromosome inactivation?
Binds to the inactive X chromosome, blocking its transcription Xist is a long noncoding RNA (lncRNA) that plays a key role in dosage compensation in females.
What is the significance of the ENCODE project?
Revealed extensive transcription of mammalian genomes and the expression of lncRNAs The project led to the development of databases like RNAcentral to store and annotate lncRNAs.
What is the estimated number of lncRNA transcripts in the human genome?
Over 170,000 lncRNA transcripts This indicates a substantial contribution to the biological complexity of higher eukaryotes.
What are the most common transposable elements in mammals?
• SINEs • LINEs These elements move to new genomic sites by reverse transcriptase.