8-Gene Expression

8-Gene Expression - Gene Expression: Transcription,...

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Gene Expression: Transcription, Processing, and Translation Chapters 13, 14 and 15 Gene Expression Overview o DNA RNA protein Crick's "Central Dogma" o BUT - not all genes encode proteins not all gene transcripts are RNA that are translated many types of RNA made Transcription o process by which the polymerization of ribonucleotides guided by complementary base pairing produces an RNA transcript from a DNA template The Transcription Unit RNA polymerases o Prokaryotes one type Core enzyme + sigma = holoenzyme o Sigma - specifically for promoter recognition o Core Enzyme - initiates transcription sigma ensures that it binds in a stable manner without sigma, has an affinity for DNA but cannot distinguish between promoter sequence and other DNA sequences o Eukaryotes three types Table 13.3, p.356
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Transcription o transcription in prokaryotes o three stages initiation elongation termination Initiation o promoter recognition o formation of transcription bubble o transition to elongation stage Bacterial Promoters o Two regions -35 region 5' TTGACA 3’ 0. plays major role in initial recognition -10 region 5' TATAAT 3’ 1. appears to be involved in melting DNA in initiation reaction 2. Pribnow box The distance separating the two regions 3. 16 - 18 bp in 90% of promoters 4. distance appears to be critical for 3-D shape of polymerase o Bacterial polymerase binds to -35 and -10 areas o Unwinding begins with -10 sequence and extends downstream through the start site Figure 13.11, p.357 Final thoughts on Initiation… o There are abortive attempts
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enzyme makes short transcripts, releases them and starts again o Initiation ENDS (elongation BEGINS) when the promoter region is cleared and the ribonucleotide chain has been extended Figure 13.13, p.358 Bacterial Elongation o Conformational change signals shift from initiation to elongation usually sigma is released polymerase no longer bound to promoter 5. rate ~40 nucleotides/second 0. compare to DNA pol III (~800 bases/sec!!) bubble stays about 12-14 nucleotides long 6. DNA-RNA hybrid ~ 8-9 bp long Bacterial Termination o Rho-dependent terminators
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extrinsic terminator 7. require a protein o Rho-independent terminators intrinsic terminator 8. do no require additional factors often hairpin loops Rho - dependent “Extrinsic terminators”
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This note was uploaded on 05/12/2008 for the course BSCI 222 taught by Professor Gdovin during the Spring '08 term at Maryland.

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8-Gene Expression - Gene Expression: Transcription,...

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