BIO206H5 Lecture Notes - Lecture 1: Operon, Alpha Helix, Recognition Sequence
Document Summary
The laci protein negatively regulates the lac operon. Be sure to include details of the molecular interactions between the protein and dna. Lac i gene is a negative repressor of lac operon because operon is turned off by regulatory protein in absence of lactose and turned on in presence of lactose. Glucose is a preferred carbon and energy source, if it is present, repressor protein binds to operator sequences to prevent transcription. Its message is constitutively expressed from its own promoter called laci promoter. The repressor protein is homotetramer composed of 4 laci proteins which bind to the operator sequences, located between promoter and start site of transcription, preventing binding of the rna polymerase. In absence of lactose, lac repressor forms a dimer which binds to the operator region and one of auxiliary region operator sequences. The two dimers form a tetramer which bends or loops, inhibiting the operon expression.