Question

The lac repressor active site The active site of the lac repressor protein is composed of OK Multiple Choice Inces O the protein domain that binds to allolactose. the protein domain that binds to DNA the protein domain that binds to other lac repressors O a glucose binding domain < Prev

Answer 1

Option A is correct.

Structurally, the lac repressor protein is a homotetramer. More precisely, the tetramer contains two DNA-binding subunits composed of two monomers each (a dimer of dimers). Each monomer consists of four distinct regions:

-An N-terminal DNA-binding domain (in which two LacI proteins bind a single operator site)
-A regulatory domain (sometimes called the core domain, which binds allolactose, an allosteric effector molecule)
-A linker that connects the DNA-binding domain with the core domain (sometimes called the hinge helix, which is important for allosteric communication)
-A C-terminal tetramerization region (which joins four monomers in an alpha-helix bundle)

*The repressor protein therefore has two binding sites, one for the lac operator (a sequence overlapping the promoter) and another for the inducer molecule (allolactose). The presence of allolactose signals the cell that lactose is available to be metabolized.