Transcription in Prokaryotes

Initiation

• Sigma factor recognizes promoter sequences at -35
• RNAP binds to promoter
    * Without sigma factor RNAP would bind loosely and randomly to DNA and not be able to initiate transcription
• The RNAP opens the DNA strand at the Pribnow box, the sigma factor disassociates, and RNA polymerase begins to synthesize RNA in the 5' ---> 3' direction

Elongation

• RNAP continues to synthesize mRNA in a 5’-->3’ direction
• In prokaryotes, operons are transcribed.
    * Operon: several related structural genes arranged under a common promoter and regulated by a common operator

Termination

• RNA polymerase reaches termination sequence
• Causes both the polymerase and newly-made RNA transcript to dissociate from DNA

Control of Gene Expression

• Transcriptional control
• Clustering of genes with related function
• Coordinate control of genes with related function
• Polycistronic mRNA