Regulation of Gene Expression in Prokaryotes

The process of DNA-dependent RNA synthesis (transcription) has been outlined in Chapter 2. RNA polymerase catalyses this reaction in which there is a 5 to 3 direction of synthesis 

This regulatory arrangement is most simply illustrated by bacterial transcription in which the structural gene is prefaced by a regulatory region including promoters that bind regulatory proteins  

The bacterial RNA polymerase has a subunit composition of ap 3 a, the a subunit being involved in correct initiation of transcription. Appropriate regulatory protein binding to the promoter region permits correct RNA polymerase binding, double-stranded DNA (dsDNA) unwinding and correct initiation of transcription. The dsDNA unwinds and the nascent RNA forms a transient RNA-DNA hybrid in the transcription bubble of unwound DNA that moves down the DNA. 

The regulation of bacterial transcription is well illustrated by the lactose operon (lac operon) of the colon bacterium Escherichia coli in which the upstream region successively (from the 5 end of the sense strand) includes a promoter (P ) for the gene (I) coding for a repressor protein (the lac repressor), a CRP binding site , the promoter for the lac operon (P), and finally an operator site (O) that prefaces the Z, Y and A structural genes of the operon  

---

Selective regulation of gene expression in prokaryotes allows the organism to respond to changing environmental factors, eg, nutrient availability, by altering the repertoire of proteins it makes. 

Chapters 30 and 31 Separate chapters devoted to the regulation of gene expression in prokaryotes and eukaryotes, respectively. 

Regulation of gene expression in prokaryotic and eukaryotic cells ... 

---