repressor In the operon theory of gene regulation, a protein produced by a regulatory gene that inhibits the activity of an operator gene, and hence switches off an operon. The action of a repressor is determined by some other factor, an effector: either this serves as a co-repressor, and hence is required to switch off the operon, or it inactivates the repressor, and so switches on the operon. See also REGULATOR GENE.

repressor In the operon theory of gene regulation, a protein produced by a regulator gene that inhibits the activity of an operator gene, and hence switches off an operon. The action of a repressor is determined by some other factor, an effector: either this serves as a co-repressor, and hence is required to switch off the operon; or it inactivates the repressor, and so switches on the operon.

repressor A protein that can prevent the expression of a gene. See operon.