The creation of milk products such as cheeses and yogurts is dependent on the conversion by various anaerobic bacteria, including several Lactobacillus species, of lactose to glucose and galactose, ultimately producing lactic acid. These conversions are dependent on both permease and β-galactosidase as part of the lac operon. After selection for rapid fermentation for the production of yogurt, one Lactobacillus subspecies lost its ability to regulate lac operon expression [Lapierre, L., et al. (2002). J. Bacteriol. 184:928–935]. Would you consider it likely that in this subspecies the lac operon is on or off? What genetic events would likely contribute to the loss of regulation as described above?

Consider the transcription of genes of the lac operon under two conditions: (1) when both glucose and lactose are present and (2) when glucose is absent and lactose is present. Describe the comparative levels of transcription of lac operon genes under these conditions, and explain the molecular basis for the difference.

In the lac operon, what are the likely effects on operon gene transcription of the mutations described in a–e?

Mutation of the CAP binding site of the lac promoter

In the lac operon, what are the likely effects on operon gene transcription of the mutations described in a–e?

Mutation of the lacI gene affecting the DNA-binding site of the protein

In the lac operon, what are the likely effects on operon gene transcription of the mutations described in a–e?

Mutation of the lacI gene affecting the allosteric site of the protein

In the lac operon, what are the likely effects on operon gene transcription of the mutations described in a–e?

Mutation of the repressor binding site on the operator sequence