BBMB 405 1st Edition Lecture 30Outline of Last Lecture XV. Chapter 29: RNA synthesis and ProcessingB. RNA polymerases catalyze transcription (con’t)C. Transcription in eukaryotes is highly regulatedOutline of Current Lecture XV. Chapter 29: RNA synthesis and ProcessingC. Transcription in eukaryotes is highly regulated (con’t)Current LectureXV. Chapter 29: RNA synthesis and ProcessingC. Transcription in eukaryotes is highly regulated (con’t)1. Riboswitches can “flip on”a. Turn on gene and can control genes that are involved in degredation or removal of metaboliteb. Moved out where concentration of adenine is low then released from complex and create terminatorc. Orphanriboswitches: predicted structure in 5’ area but don’t know purpose/ligand, in front of genes, none of predicted ligands bindd. Orthogonal riboswitches: researchers take naturally occurring and do in vitro evolution experiment, create riboswitch that can bind to molecule not found in natural cell2. TATA box versus CpG island promotersThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.a. Defined transcription start site within Initiator sequenceb. TATA box is recognized by TBP without additional factorsc. Found in tissue specific promotersd. Can have multiple transcription start sites leading to mRNAs with different 5’-UTRse. TATA box is binding by TBP is assisted by additional transcription factorsf. Found in promoters for housekeeping genes3. Formation of preinitiation complex by general transcription factorsa. Transcription factor IID (TFIID): TBP and 16 TBP-associated factors (TAFs) bind the TATA boxb. TFIIB: important for start site selectionc. TFIIE: facilitates DNA unwindingd. TFIIH: Complex of 10 subunits, including helicases (involved in DNA unwinding) and kinases (involved in Pol II C-terminal phosphorylation)e.4. Many RNAs are processed post-transcriptionally5. Polycistronic pre-rRNAs transcripts must be cleaveda. Cleavage is dependent on the U3 small nucleolar RNA (snoRNA- bind and present functional region) containing 2.5 MDa small-subunit (SSU- essential in forming ribosome) processomeb. Cistron = gene; polycistron = multiple genes; polycistronic transcript = multiple genes within a single transcriptc. Pre-RNA is folded and assembled in nucleolus (very dense granule localized as sight for RNA construction, not bound by membrane)d. Why RNA used to make RNA? RNA really big, ensures right cleavage site6. Modificationa. Involves snoRNAb. Types: methylation of nucleobase or ribosec. Important in structure and stabilityd.e.f. Effects on structure (above)7. Transfer RNA processinga. Leader sequence: cleaved off so can be function, cleaved by RNase P (multi-turnover enzyme, release product and catalyze reaction- recycle self)b. Triming of 3’ end and addition, added by CCA enzyme, attach amino acid to sitec. May contain introns that have to be spliced out; splicing by endonuclease, kinase and RNA ligase (eukaryotes and archaea) or through self-splicing (bacteria)8. RNase P is a multi-turnover ribozyme9. Eukaryotic pre-mRNA processinga. Tag at 5’ end: - Bacteria keeps triphosphate; eukaryote gets modified- Begin with triphosphate- first step is gamma phosphate is removed (RNA triphosphatase)- Add GTP via mRNA guanylyltransferase- Use SAM to methylate G via guanylyl-N7-methyltransferase- Protection: resembles 3’ end instead because have a base rather than a phosphate- Important in recognition-b. 3’ end (3’-polyadenylation)- Stabilizes mRNA and enhances translation- Protects through binding of poly A binding protein which coats end- Acts as signal for recruitment of transcription factors- Can introduce
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