Describe the regulation of gene expression in prokaryotes with an example.

(N/A) In prokaryotes,the regulation of gene expression is primarily achieved by controlling the rate of transcriptional initiation.
The activity of $RNA$ polymerase at a given promoter in a transcription unit is regulated by the interaction with accessory proteins,which affect the ability to recognize start sites.
These regulatory proteins can act both positively (activators) and negatively (repressors).
The accessibility of promoter regions in prokaryotic $DNA$ is,in many cases,regulated by the interaction of proteins with specific sequences termed $operators$.
In most cases,the operator is located adjacent to the promoter element. Each operon has its specific operator and specific repressor. For example,the $lac$ operator is present only in the $lac$ operon and it interacts specifically with the $lac$ repressor.