In the lac operon,the $z$ gene codes for:

Which of the following binds to the repressor,causing the repressor and the operator to dissociate from each other?

In eukaryotes,the regulation of gene expression could be exerted at $:-$
$(I)$ Transcriptional level (formation of primary transcript)
$(II)$ Processing level (regulation of splicing)
$(III)$ Transport of $\text{mRNA}$ from nucleus to the cytoplasm
$(IV)$ Translational level
Choose the correct order for given statements $:-$

Match List-$I$ with List-$II$.

List-$I$	List-$II$
$A$. Gene $a$	$I$. $\beta$-galactosidase
$B$. Gene $y$	$II$. Transacetylase
$C$. Gene $i$	$III$. Permease
$D$. Gene $z$	$IV$. Repressor protein

Choose the correct answer from the options given below:

In $lac$ operon,the switching on or switching off of the operator is achieved by . . . . . . .

Assertion $(A):$ Regulation of $lac$ operon by repressor is referred to as negative regulation.
Reason $(R):$ Repressor protein binds to the operator region and prevents $\text{RNA}$ polymerase from transcribing the operon.