Transcription II

Transcription II - Transcription in Prokaryotes In E.coli,...

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Transcription in Prokaryotes In E.coli, RNA polymerase is a 465 kD complex, with 2 α , 1 β , 1 β ', 1 σ (holoenzyme). Core enzyme is 2 α , 1 β , 1 β ’ (can transcribe but it can’t find promoters). σ recognizes promoter sequences on DNA; β ' binds DNA; β binds NTPs and interacts with σ . α subunits appear to be essential for assembly and for activation of enzyme by regulatory proteins. RNA Polymerase Has Many Functions • Scan DNA and identify promoters • Bind to promoters • Initiate transcription • Elongate the RNA chain • Terminate transcription • Is responsive to regulatory proteins (activators and repressors) RNAP is a multisubunit enzyme
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RNA polymerases have the following properties: 1. the enzymes are template dependent, requiring double-stranded DNA 2. the enzymes do not require a primer; synthesis begins with a nucleoside triphosphate 3. the enzymes require the four nucleoside triphosphates (ATP, GTP, CTP, and UTP). 4. the enzymes copy (read) the template DNA strand in the 3' to 5' direction. 5. the enzymes synthesize the RNA in the 5' to 3' direction In the prokaryotic world only one enzyme is necessary to carry out all of the transcription of RNA from DNA, catalyzing the synthesis of messenger RNA, ribosomal RNA, and transfer RNA.
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αΙ β β αΙΙ σ 70 RNAP HOLOENZYME - σ 70 Promoter-specifc transcription initiation In the Holoenzyme: · β ' binds DNA · β binds NTPs · β and β ' together make up the active site · α subunits appear to be essential For assembly and For activation oF enzyme by regulatory proteins. They also bind DNA. · σ recognizes promoter sequences on DNA Sigma factor is a specificity factor. The holoenzyme, because of sigma, is able to bind specific DNA Sequences called promoters and initiate RNA synthesis
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α α 2 α 2 β α 2 ββ ’ = core enzyme αΙ β β αΙΙ CORE ENZYME Sequence-independent, nonspecifc transcription initiation + vegetative (principal σ ) σ 70 SIGMA SUBUNIT interchangeable, promoter recognition The assembly pathway of the core enzyme heat shock (For emergencies) σ 32 nitrogen starvation (For emergencies) σ 60 Properties of Promoters Promoters typically consist of a 40 bp region on the 5'-side of the transcription start site Two consensus sequence elements: The -35 region, with consensus TTGACA The -10 region, with consensus TATAAT “Pribnow box” this region is ideal for unwinding.
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Transcriptional start site +1 –35 sequence 16–19 bp –10 sequence Promoter region G T C A T A C G A T A T T A T A T A T A A T A T A T 3 5 5 3 Transcription 5 3 RNA A Coding strand Template strand Please note that these are features of the general Sigma70 promoter
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This note was uploaded on 03/16/2010 for the course BIO 362 taught by Professor Walikarzai during the Spring '10 term at SUNY Stony Brook.

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Transcription II - Transcription in Prokaryotes In E.coli,...

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