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Medical Definition of Lactose repressor
1. Protein (tetramer of 37 kD subunits) that normally binds with very high affinity to the operator region of the lactose operon and inhibits transcription of the downstream genes by blocking access of the polymerase to the promoter region. When the lactose repressor binds allolactose, its binding to the operator is reduced and the gene set is derepressed. This entry appears with permission from the Dictionary of Cell and Molecular Biology (11 Mar 2008)