In the absence of glucose, the cap protein binds to a dna sequence adjacent to the promoter of the lac operon. binding of cap rna polymerase to bind to the promoter and allows for a high level of transcription of the lac operon. regulation of the lac operon by the cap protein is an example of

Positive regulation

Explanation:

CAP, the catabolite activator protein is a positively acting regulator protein. It is activated when bound to cAMP; active CAP stimulates transcription of the lac operon.  

In the absence of glucose, the cAMP levels of the cell are increased which in turn binds to the CAP to form the cAMP-CAP complex. The cAMP-CAP complex binds to the binding site present near the promoter of the lac operon. This binding strengthens the affinity of the promoter for RNA polymerase and thereby accelerates the expression of the lac operon in the presence of lactose.