Lac operon is:

In the lactose operon of $Escherichia \text{ } coli$, what is the function of the promoter?

Transposons can be used during which one of the following?

The functional complex that consists of a cluster of genes including structural genes,a promoter gene,an operator gene,and a regulator gene was discovered by:

$A$: $Lac$ operon exerts negative control only.
$R$: The operator is occupied by aporepressor during regulation.

$A$ low level of expression of lac operon occurs at all the time. Can you explain the logic behind this phenomenon?