EXAM III Drs. Questions 1 - 33 are all multiple choice, each worth three points. I, Z, Y, and A are structural genes. The lac repressor is encoded by I. Z encodes beta-galactosidase, needed to cleave lactose into galactose and glucose.
Y encodes a permease, a transport protein needed to get lactose into the cell.
On the DNA are also an operator for the lac operon, O lac , and a promoter, P lac . There is also a promoter, Pi, for the I gene. The system is regulated by the presence of lactose and the absence of glucose. An E. coli strain has a mutation in the lacI structural gene that generates a stop codon five codons into the coding sequence. The presence of glucose will not affect transcription.