Chapter 16, Problem 28P

For each of the E. coli strains that follow, indicate the effect of the genotype on the expression of the trpE and trpC genes in the presence or absence of tryptophan. [In the wild type (R⁺ P⁺ o⁺ att⁺ trpE⁺ trpC⁺), trpC and trpE are fully repressed in the presence of tryptophan and are fully expressed in the absence of tryptophan.]

R = repressor gene; Rⁿ product cannot bind tryptophan; R^- product cannot bind operator

o = operator for the trp operon; o^- cannot bind repressor

att = attenuator; att^- is a deletion of the attenuator

P = promoter; P^- is a deletion of the trp operon promoter

trpE⁻ and trpC^- are null (loss-of-function) mutations

a. R+ P- o+ att+ trpE+ trpC+

b. R- P+ o+ att+ trpE+ trpC+

c. Rn P+ o+ att- trpE+ trpC+

d. R- P+ o+ att- trpE+ trpC+

e. R+ P+ o- att+ trpE+ trpC- /R- P+ o+ att+ trpE- trpC+

f. R+ P- o+ att+ trpE+ trpC- /R- P+ o+ att+ trpE- trpC+

g. R+ P+ o- att- trpE+ trpC- /R- P+ o- att+ trpE- trpC+