Question

Riboflavin is a B vitamin synthesized by the bacteria B. subtilis. The four genes required for riboflavin biosynthesis are clustered in the rib operon. The expression of the operon is dependent on the availability of riboflavin and is controlled by the regulator protein, RibC. When present in the environment, Riboflavin binds to the regulatory protein. m2 (ribo r z @ riboribb riba ribH Use this information to respond to the following questions. A. Is the rib operon expressed when riboflavin is present or absent? Explain in 1 or 2 sentences. (2 pts) B. Assume the regulatory protein, RibC, is an activator. Explain the mechanism by which riboflavin would INCREASE transcription of the rib operon in 1 or 2 sentences. (2 pts) C. Assume the regulatory protein, RibC, is a repressor. Explain the mechanism by which riboflavin would DECREASE transcription of the rib operon in 1 or 2 sentences. (2 pts)

Answer 1

Answer-1 Rib protein is not expressed when riboflavin is present in the environment as anabolic pathways are mostly regulated by repressible operon. Answer-2 Rib C will bind to riboflavin which will cause its activation and then this complex will bind to another regulatory sequence on the operon thus increasing the transcription by chromosomal remodelling. Answer -3 Rib C will bind to the riboflavin which will cause the activation of the ribC repressor thus it will bind to operator and will hinder the binding of DNA polymerase