Recall that the Trp repressor binds to a site in the operator region of tryptophan-producing genes when tryptophan is abundant, thereby preventing transcription. What would happen to the expression of the tryptophan biosynthetic enzyme genes in the following scenarios? Fill in the blanks with one of the following phrases:

never be expressed/always (constitutively) be expressed

a. The cell produces a mutant Trp repressor that cannot bind to the operator. The enzyme genes will ______ _.

b. The cell produces a mutant Trp repressor that binds to its operator site even if no Tryptophan in present. The enzyme genes will ______ _.

c. The cell produces a mutant, sigma factor that cannot bind the promoter region. The enzyme genes will ____ _.

d. Elongation of the leader sequence is always stalled after transcription of region 1. The enzyme genes will _____ _.