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Lecture 34-35: Gene Regulation (lncRNAs (Genomic Imprinting: Alleles or…
Lecture 34-35: Gene Regulation
In bacteria: functionally related proteins are produced from a single transcript. The transcription of an operon is regulated by proteins that bind to an operator
Transcription of eukaryotic genes is regulated by proteins that bind at many sites (enhancers) located in and around genes
Enhancer: cis-acting (on gene next to them) DNA sequence that can elevate levels of transcription- bound to different enhancer sequences
These enhancers show combinatorial control of transcription
Depending on available ambient factors, different genes are expressed/not expressed
Can be upstream, downstream, or even in an intron
Histones
Acetylation or methylation of specific amino acids in the tails affect DNA compaction, controls accessibility of genes to transcription factors.
Heterochromatin= bunch of histones, no transcription
Tails have amino acids available for chemical modification
Euchromatin= transcription
Dna methylation represses gene expression; histone acetylation promotes gene expression
Changes in DNA methylation play a major role in cancer
The environment can have an effect o methylation
lncRNAs
Genomic Imprinting: Alleles or chromosome sets are silenced in somatic cells
Stem Cell self-renewal, differentiation, & re-programming
X inactivation
Plants:
Mammals:
Flowering time
In females, one X-chromosome is randomly inactivated
X inactivation center (XIC) transcribes Xist noncoding RNA, spreads along chromosome
The Xist RNA triggers histone methylation, which impedes transcription
Tsix, a lncRNA, inhibits Xist transcription
How Xist works: binds to PRC2, which adds three methyls to lysine and inhibits transcription
MicroRNAs: repress translation, promote RNA decay
Binds to sites in 3'UTR in animals
Dicer readies the miRNA to bind to DNA strand
Proteins destined to be degraded are marked with ubiquitin
Protein will enter proteasome & be degraded
The amount of a protein is determined by the rate of:
Translation
Degradation of mRNA or protein
Transcription
The amount of a protein is determined by:
Protein Cleavage
Protein Modifications (phosphorylation, glycosylation, methylation, acetylation, etc.)