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Chapter 11 - Transcription and Translation

Promoter is where rna polymerase binds to prior to

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Unformatted text preview: e RNA polymerase binds to prior to transcription Once polymerase has finished adding nucleotides, the DNA-RNA hybrid dissociates and the DNA double helix reforms There is one type of RNA polymerase contains 5 subunits associated to form a core enzyme If we purify the core enzyme, and place in a test tube with nucleotides and DNA: it synthesizes RNA, but RNA is made from random sites in the DNA Prokaryotic Transcription o o o o If we purify an accessory polypeptide, normally associated in vivo, transcription begins at correct locations only Sigma factor matches in vivo transcription Attachement of Sigma: increases affinity for promoter sites in DNA, decreases affinity for DNA in general RNA polymerase can now slide freely along DNA until it recognizes and binds a specific promoter Initiation of Transcription in bacteria o o o Loose association between DNA and core enzyme occurs RNA chains that are begun are not initiated at the proper sites The association of the complete enzyme with DNA at proper site occurs and then the double helix opens The sigma factor is lost as RNA chain is elongated Prokaryotic Promoters o o o o o Located upstream (5 ) from transcript initiation site Pribnow box (TATAAT) Many genes also have a consensus sequence TTGCCA at about 35 base pairs in 5 direction Differences in Pribnow box or -35th element may regulate gene transcription Can have a variety of sigma factors recognize different versions of promoter sequence; cells can control how much of ea...
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