Becker's World of the Cell 9th Edition by Lewis Kleinsmith, Jeff Hardin, Gregory Paul Bertoni

Exercise 10

Antibiotic Inhibitors of Transcription. Rifamycin and actinomycin D are two antibiotics derived from the bacterium Streptomyces. Rifamycin binds to the /3 subunit of E. coli RNA polymerase and interferes with the formation of the first phos- phodiester bond in the RNA chain. Actinomycin D binds to double-stranded DNA by intercalation (slipping between neighboring base pairs).
(a)Which of the four stages in transcription would you expect rifamycin to affect primarily
(b)Which of the four stages in transcription would you expect actinomycin D to affect primarily
(c)Which of the two inhibitors is more likely to affect RNA synthesis in cultured human liver cells
(d)Which of the two inhibitors would be more useful for an experiment that requires the initiation of new RNA chains to be blocked without interfering with the elongation of chains that are already being synthesized
(e)When fertilized sea urchin eggs are treated with actinomycin D, they develop for many hours but eventually arrest as hollow balls of several hundred cells (called blastulae). Propose an explanation for why such embryos arrest, but also why they progress as far as they do.