Which of these would characterize such a mutant?

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Which of these would characterize such a mutant?

There is a mutation in the repressor that results in a molecule known as a super-repressor because it represses the lac operon permanently. Which of these would characterize such a mutant?

1. It makes a repressor that binds CAP.
2. It cannot bind to the operator.
3. It cannot make a functional repressor.
4. It cannot bind to the inducer.

Related info

The lactose manipulator is a group of genes involved in lactose catabolism. It is composed of blockers and manipulator sequences of the lactose system, which allows the synchronized regulation of a group of genes related to lactose metabolism.

Structure of Lac operon and negative regulation diagram:

The famous manipulator theory was proposed by F. Jacob and J. Monod in 1961 based on the study of this system.

In the manipulon of the lactose system of E. coli, the structural genes of β-galactosidase, galactosidase permease, and galactosyltransferase are arranged on the plasmid in the order of LacZ (z), Lac Y (y), and Lac A (a), respectively. Upstream of z is the manipulator sequence Lac O (o), and further upstream is the promoter Lac P (p).

This is the structural pattern of the manipulator (lactose manipulator). The regulatory gene Lac I (i), which encodes a deterrent in the lactose manipulation system, is located in close proximity to and upstream of p.

Structural genes of related functions in bacteria are often linked together to form a gene cluster. They encode different enzymes in the same metabolic pathway.

A gene cluster is regulated by the same regulation, one open and one closed. This means that they form a single regulated unit. Other genes with related functions are also included in this regulatory unit.

For example, the gene encoding a permease, whose product is not directly involved in catalytic metabolism, allows the transport of small molecule substrates into the cell.

Three genes associated with lactose catabolism metabolism, lacZ, Y and A, are very typical of the above mentioned gene cluster. Their products catalyze the catabolism of lactose, producing glucose and galactose. They have a cis-acting regulatory element and a corresponding trans-acting regulatory factor.

The product of lac I, called lac repressor, functions by binding to the manipulator gene (lac O) at the 5′ end of the lacZ, Y, and A gene cluster, which is located between the promoter (lac P) and the structural gene (lac ZYA).

When the repressor binds to the manipulator gene it blocks the transcription start on the promoter. lac O extends from the mRNA transcription start site upstream of -5 to the transcription unit +21. In this way it overlaps with the end of the promoter.

Newer ideas suggest that the blocker affects RNA polymerase. From the point of view of the relevant positions of both the manipulator gene and the promoter, the binding of the repressor to the DNA prevents RNA polymerase from transcribing the structural gene.

However, we must note that some other manipulator genes on the manipulator are not in the same position as the lactose manipulator, and thus the blocker protein can bind to the manipulator gene to block transcription in multiple ways.

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