HNO₂ or Nitrous Acid is deaminating agent causes removal of –NH2 for nitrogenous bases. 

TLS Online TPP Program

#Id: 572

#Unit 2. Cellular Organization

Repressor binds with O1and O3 tonhibit expression of lacZ

TLS Online TPP Program

#Id: 573

#Unit 2. Cellular Organization

Effects of mutations in the three lac operators

All three operators are essential for effective repression.

TLS Online TPP Program

#Id: 574

#Unit 2. Cellular Organization

OC are constitutive because repressor protein is unable to bind; this allows RNA polymerase to have unrestrained access to the promoter. 

TLS Online TPP Program

#Id: 575

#Unit 2. Cellular Organization

The Oc mutations are cis-acting/cis dominant, because they affect only the contiguous set of structural genes.

 

TLS Online TPP Program

#Id: 576

#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: 577

#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.