Read this article to learn about the three types of mutations helpful in determining the role of a particular gene.
The three types of mutations are: (1) Operator Mutations (2) Repressor Mutations and (3) Structural Gene Mutations.
A mutation in any sequence of promoter or structural gene results in changed gene expression, e.g., altered protein, non-transcription etc. Some of the mutations are expressed below. These mutations are helpful in determining the role of a particular gene.
Some of the important mutation which are helpful in determining the role of a particular gene are as follows:
1. Operator Mutations:
The operator is a specific DNA sequence that is recognized by the lac- repressor protein. If this sequence changes (mutates) to a sufficient degree, the repressor can no longer bind to it. This type of operator mutation is denoted by Oc. The “c” stands for constitutive, since this type of operator mutation allows the Operon to be constitutively transcribed (always ‘on’ position). Operator mutations act in a cis-dominant mode, such that they are not overcome by introducing a normal copy of the gene in a merozygote.
2. Repressor Mutations:
Mutations that result in the repressor protein being unable to bind the operator locus (denoted I-) will always be recessive when in trans to a wild type copy of the gene, whose product will bind to both operators. Repressor protein mutations that are unable to bind allolactose (denoted IS) will remain bound to the operator locus, and will be dominant in trans.
3. Structural Gene Mutations:
A mutation that blocks the activity of β-galactosidase will prevent the conversion of lactose to allolactose. Induction of the Operon by lactose will be blocked, but externally supplied allolactose will still serve as an inducer. The induced Operon will not generate a functional P-galactosidase, but the other two enzymes will be induced normally. A mutation that blocks the activity of the permease will block (or greatly impair) all induction unless artificial means are employed to get lactose into the cell.