The E. coli trp operon contains the 5 genes Trp-EDCBA for the anabolic enzymes to make the tryptophan.

TLS Online TPP Program

#Id: 6383

#Unit 2. Cellular Organization

TLS Online TPP Program

#Id: 6384

#Unit 2. Cellular Organization

The DNA-binding domain occupies residues 1–59. It contains two a-helices separated by a turn. This is a common DNA-binding motif known as the HTH (helix-turn-helix); the two a-helices fit into the major groove of DNA

TLS Online TPP Program

#Id: 6385

#Unit 2. Cellular Organization

Promoter mutations are also cis-acting. If they prevent RNA polymerase from binding at P-lac, the structural genes are never transcribed.

TLS Online TPP Program

#Id: 6386

#Unit 2. Cellular Organization

Mutants that cannot be expressed at all are called uninducible. Mutants that are continuously expressed are called constitutive mutants.

TLS Online TPP Program

#Id: 6387

#Unit 2. Cellular Organization

Cryptic mutants” of lac operon make b-galactosidase but still could not grow on lactose means they are essentially Y-

TLS Online TPP Program

#Id: 6388

#Unit 2. Cellular Organization

Catabolite repression is exerted through a second messenger called cyclic AMP (cAMP) and the positive regulator protein called the catabolite repressor protein (CRP), a dimer.