A second bacterial operon is the tryptophan operon, or trp operon. This operon is usually turned on because the cell needs to make the amino acid tryptophan. Once trp has bound to the repressor, it becomes active and binds to the operator, stopping any transcription. Eukaryotic Gene Regulation. Eukaryotic processes are more complicated than those which occur in bacteria, and can occur at a variety of stages.
Transcription regulation involves transcription factors such as activators or repressors.
Activators are proteins that bind to enhancers, DNA sequences far away from the gene to be transcribed. Conversely, repressors bind to silencer DNA sequences and prevent RNA polymerase from initiating transcription. When genes in a metabolic pathway are on different chromosomes, the same activators bind to each gene, wherever it is located. Then transcription can occur simultaneously. Transcription regulation also involves modifying RNA transcripts.