1) Agent 2) An agent that represses 3) Represser 1) Represser 
a DNA-binding protein that regulates the expression of one or more genes by binding to the operator and blocking the attachment of RNA polymerase to the promoter, thus preventing transcription of the genes.
In molecular genetics, a repressor is a DNA- or RNA-binding protein that inhibits the expression of one or more genes by binding to the operator. A DNA-binding repressor blocks the attachment of RNA polymerase to the promoter, thus preventing transcription of the genes into messenger RNA. An RNA-binding repressor binds to the mRNA and prevents tra...
(from the article `gene`) ...genes are linked to an operator gene in a functional unit called an operon. Ultimately, the activity of the operon is controlled by a regulator ... Formation of -galactosidase has been shown to be controlled by a so-called regulator gene presumed to specify a protein, called a repressor protein, ... ...re...
A protein that regulates a gene by turning it off.
A DNA-binding protein in prokaryotes that blocks gene transcription by binding to the operator.
A type of protein molecule that binds to DNA that shuts up transcription of a gene. See: operon or operator. ... (09 Oct 1997) ... 
(re-pres´әr) that which restrains or inhibits; a specific protein molecule coded for by a regulatory gene, which acts through the cytoplasm to repress the synthesis of a specific protein. in genetics, a protein produced by a regulator gene that binds to the operator region of a structural gene to blo...
Type: Term Pronunciation: rē-pres′ŏr Definitions: 1. The product of a regulator or repressor gene; a molecular entity that prevents the transcription of regulator genes under control of an operator.
[n] - an agent that represses
protein that suppresses transcription of a gene or operon in response to an external stimulus
represser noun an agent that represses