Question

4. Answer the following concerning promoters and transcription. (15 points) a. What role do promoters play in transcription? b. What is the common structure of a bacterial promoter with respect to its consensus sequences? c. What is the role of the sigma subunit for bacterial RNA polymerase as it relates to promoters? d. Eukaryotic promoters are more variable than prokaryotic promoters. Explain why e. Explain what would happen to a eukaryotic promoter if it were associated with acetylated

Answer 1

a. A promoter is a cis-acting element. It is the site where RNA polymerase binds and initiates transcription.

b. A bacterial promoter contains two elements.

-35 element = 5'-TTGACA-3'

-10 element = 5'-TATTAT-3'

c. Sigma subunit is a bacterial transcription factor that is essential for specific binding of RNA polymerase to the promoter. It is involved in the initiation of transcription.

d. Eukaryotes show complex gene regulation mechanism than prokaryotes. Each gene is regulated by multiple factors which bind to different cis elements. hence, eukaryotic promoters are more diverse than prokaryotes.

e. Histones are basic proteins that wrap around the DNA to form the chromatin. Histone tails are subjected various post-translational modifications which alter their binding affinity to the DNA. Acetylation increases negative charge on histones. So, acetylated histones can not strongly bind to DNA as DNA is also a negatively charged molecule (due to the presence of phosphate groups). Hence promoter that contains acetylated histones is loosely packed.