text: Repressor proteins bind to the DNA strand and prevent RNA polymerase from being able to attach to the DNA and synthesize mRNA. Inducers bind to repressors, causing them to change shape and preventing them from binding to DNA. Therefore, they allow transcription, and thus gene expression, to take place.
  For a gene to be expressed, its DNA sequence must be copied (in a process known as transcription) to make a smaller, mobile molecule called messenger RNA (mRNA), which carries the instructions for making a protein to the site where the protein is manufactured (in a process known as translation). Many different types of proteins can affect the level of gene expression by promoting or preventing transcription. In prokaryotes (such as bacteria), these proteins often act on a portion of DNA known as the operator at the beginning of the gene. The promoter is where RNA polymerase, the enzyme that copies the genetic sequence and synthesizes the mRNA, attaches to the DNA strand.
  Some genes are modulated by activators, which have the opposite effect on gene expression as repressors. Inducers can also bind to activator proteins, allowing them to bind to the operator DNA where they promote RNA transcription.
  Ligands that bind to deactivate activator proteins are not, in the technical sense, classified as inducers, since they have the effect of preventing transcription.