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DevelopmentW2010.Lecture3notes

DevelopmentW2010.Lecture3notes - Development BIO 120 Winter...

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Development BIO 120 Winter 2010 Jeremy Lee Patrick Yuh Eva Murdock Lecture 3 Differential Gene Expression: Transcriptional Regulation I. Molecular Mechanisms Underlying Differential Gene Expression (Figs. #1, #2)) a. Transcriptional regulation : determination of when, and in which cells, a gene is transcribed to RNA. b. Transcript processing : alteration of primary RNA transcript to mRNA. Includes addition of 5’ cap, addition of polyA tail by the enzyme polyA polymerase, and removal of introns and splicing of exons. Structure of mRNA includes 5’cap, 5’ UTR, start codon, open reading frame (coding region), stop codon, 3’ UTR, polyA tail. c. Selective translation : determination if/when mRNA is translated to protein in each cell. d. Protein modification : functional alteration and/or transport of protein to site of action. II. Transcriptional Regulation through cis Regulatory Elements: Promoters and Enhancers a. Promoter : DNA sequences within a gene required for binding of RNA polymerase II . Promoter is usually found immediately upstream of transcription initiation site . Also, promoter usually binds basal transcription factors that are required for a "basal level" of transcription" (Fig. #3) b. Enhancer : DNA sequences in a gene that frequently are found upstream of the promoter (Fig. #4), though they can also be at the 3' end of the gene or within an intron. Enhancers bind specific transcription factors (see below), which are proteins that modify the rate and efficiency of transcription. 1. Positive enhancer : binds specific transcription factors that activate (increase level or rate of) transcription. (Frequently positive enhancers are just referred to simply as “enhancers.”) 2. Negative enhancer = silencer: binds specific transcription factors that repress (decrease level or rate of) transcription. c. A basal level of transcription involves the formation of the transcription pre-initiation complex (Fig. #5.1– 5.3) 1. The general transcription factor TFIID binds to the promoter. In most genes this involves the TATA binding protein (TBP) subunit of TFIID binding to the TATA box of the promoter. 2. Other general transcription factors, including TFIIA, TFIIB and TFIIH, join the complex. 3. RNA polymerase II , the enzyme that catalyzes transcription of protein-encoding genes in eukaryotes, is bound by the general transcription factors TFIIE and TFIIF . The entire complex, made up of the enzyme plus these transcription factors, is then positioned on the promoter by TFIIB.
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