Definition of Lac Repressor

Lac repressor is a protein that gets bound to the operator site of the lac operon and is responsible for inhibiting the process of transcription. It is typically a tetramer of protein in which there are four identical components are present, each having a length of 360 amino acids. The lac repressor has a molecular weight of 154,520 Daltons when the components are associated in order to form an active tetrameric form.


This lac repressor gets bind to the promoter region of the palindromic sequence of DNA. It gets attached to the NH2 terminal of the DNA. They inhibit the expression of genes that are involved in the metabolism of lactose in the bacteria. The genes are repressed under the non-availability of the lactose.

View More Genetics Definitions