The Bacterium, Bacillus Subtilis, Can Grow on Minimal Media with a Variety

question 43

Essay

The bacterium, Bacillus subtilis, can grow on minimal media with a variety of sugars as its carbon source.One such sugar is mannose, metabolized by the products of the man operon.Expression of the operon is controlled by a regulatory protein encoded in a separate gene, manR.Depending on conditions, the regulatory protein may bind at one of two sites in the operon, as follows:
(i)When mannose is absent from the cell, the regulatory protein is in a conformation called R1.R1 can bind specifically at an operator site manO.Binding of R1 at manO reduces transcription of the operon four-fold from a basal level of 20 units.
(ii)When mannose is present in the cell, it binds to the regulatory protein, causing it to undergo an allosteric transition from conformation R1 to a new conformation, called R2.R2 cannot bind at manO.However, R2 can bind specifically at a different site called the initiator, manI.Binding of R2 at manI increases transcription of the operon two-fold from the basal level.
Mutations, m1-m3, which affect expression of this operon, were identified.Each mutation affects only a single component of the operon.Levels of operon activity were measured in haploids.They were also measured in partial diploids with an F' carrying the wild-type alleles of all genes and regulatory elements described above. For each mutation, describe which component is affected.In addition, explain the observed activity in the haploid and partial diploid in each case.

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