Answer:
a regulatory protein binds to DNA which blocks transcription
Step-by-step explanation:
Negative control of gene expression includes the binding of certain regulatory proteins to the regulatory sequences. This binding prevents the expression of certain sets of the gene. For instance, binding of repressor protein to the operator sequence of lac operon prevents the expression of structural genes of the operon. This pattern of gene regulation is called negative regulation. The binding of the repressor to the operator sequence does not allow the RNA polymerase to transcribe genes since the operator and promoter (binding site for RNA polymerase) sequences are present in close vicinity.