Which organism was used by Beadle and Tatum to propose the one gene-one enzyme hypothesis?

In the $lac$ operon,if a nonsense mutation occurs in the $lac\, y$ gene,which enzymes will be synthesized?

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:

An $E. coli$ cell with a mutated $z$ gene of the $lac$ operon cannot grow in a medium containing only lactose as the source of energy because:

The accessibility of promoter regions of bacterial $DNA$ in many cases is regulated by the interaction of proteins with sequences termed:

Which of the following is not a component of the $Operon$ model?