6. The o subunits enable the coli RNA polymerase to recognize specific promoter sites o The rna polymerase without the o subunit (i.e, the a2BBo) is unable to start transcription at a promoter o The o subunit decreases the affinity of rna polymerase for general(non-promoter) regions of dna by a factor of 10 o E coli contains multiple o factors for recognizing different promoters, e.g.,o for standard promoters; 32 for heat-shock promoters; o54 for nitrogen starvation promoters o Each type of o factor allows the cell to coordinately express a set of genes
6. The s subunits enable the E.coli RNA polymerase to recognize specific promoter sites ⚫ The RNA polymerase without the s subunit (i.e., the a2bb’) is unable to start transcription at a promoter. ⚫ The s subunit decreases the affinity of RNA polymerase for general (non-promoter) regions of DNA by a factor of 104 . ⚫ E.coli contains multiple s factors for recognizing different promoters, e.g., s70 for standard promoters; s32 for heat-shock promoters; s54 for nitrogenstarvation promoters. ⚫ Each type of s factor allows the cell to coordinately express a set of genes
E coli contains multiple o factors for recognizing different types of promoters: 35 5'MTTGACAwTATAATw3+Standard 5'MTNNCNCNCTTGAAwCCCATNTw3+-Heat-shock 5'MCTGGGNAMT TGCAN3 ogen rvation 0 for standard promoters 032 for heat-shock promoters oo4 for nitrogen-starvation promoters
Standard Heat-shock Nitrogen starvation s70 for standard promoters; s32 for heat-shock promoters; s54 for nitrogen-starvation promoters E.coli contains multiple s factors for recognizing different types of promoters:
7. RNA polymerase unwinds the template DNA then initiate RNA synthesis The enzyme slides to a promoter region and forms a more tightly boundclosed complex? o Then the polymerase-promoter complex has to be converted to an"open complex, in which a 12-15 bp covering the region from the aT-rich -10 site to +3 site is unwound The essential transition from aclosed to an"open complex sets the stage for RNa synthesis, after which the core polymerase moves away from the promoter
7. RNA polymerase unwinds the template DNA then initiate RNA synthesis ⚫ The enzyme slides to a promoter region and forms a more tightly bound “closed complex”. ⚫ Then the polymerase-promoter complex has to be converted to an “open complex”, in which a 12-15 bp covering the region from the AT-rich –10 site to +3 site is unwound. ⚫ The essential transition from a “closed” to an “open” complex sets the stage for RNA synthesis, after which the core polymerase moves away from the promoter. random
Binding Initiation 二—二 3 Initiation of transcription 5 UP-35-10+1 Closed complex formation 二 Promoter clearance Open com formation Initiation 二二
