What effect would the following mutations have upon LacZ exp

What effect would the following mutations have upon LacZ expression in Escherichia coli in the presence or absence of lactose? LacI^- (no LacI protein made) LacO^-(no lactose operator sequence) Predict the expression of LacZ in each of these mutants if a plasmid containing a good copy of LacI were introduced into them. Please explain your responses.

Solution

Condition 1. When LacI gene is mutated-

Lac I gene translate a protein called as repressor which upon tetramerization binds to operator region and thus repress the gene expression of LacZ gene.

When there is the mutation in LacI gene then in that condition there will not any regulation of Lac Z gene and as a result of it, there will constitutively expression of LacZ gene.

Condition 2. When there is mutation in LacO-(no lactose operator sequence-

As we know that Lac I gene translate a protein called as repressor which upon tetramerization binds to operator region LacO and thus repress the gene expression of LacZ gene.

Since there is repressor protein in the cell but there is no binding site for it. In that condition, there will not any regulation of Lac Z gene and as a result of it, there will constitutively expression of LacZ gene.

Condition 3. If a plasmid containing a good copy of LacI were introduced into them -

In the caseWhen LacI gene is mutated- the normal repressor will be form from the normal Lac I plasmid and as a result of it there will be production of repressor. Repressor will bind to the operator site and repress the expression of Lac Z gene.

In the case there is mutation in LacO- since there is mutation in Operator site so there won\'t be any repression as there is no site for the binding of repressor that is synthesised by the introduce plasmid