What is the function of LacI gene?

The Lactose inhibitor,” LacI, is a DNA-binding transcription factor that represses transcription of the operon involved in transport and catabolism of lactose .

What is the function of LacI in the regulation of the lac operon?

What is the function of lacI in the regulation of the lac operon? It is a structural gene that encodes permease. It is the promoter that mediates the transcription of the operon. It encodes a repressor that, in the absence of lactose, binds to the lac operator and blocks expression of the structural genes.

What protein does LacI code for?

the lac repressor
A key to controlling the operon is the DNA-binding protein called the lac repressor (LacI), shown on the left. In the absence of lactose, LacI inhibits the expression of the operon by binding to two out of three operator sites and causing the DNA between the bound sites to fold into a loop.

What does LacI mean genetics?

The lacI locus – One type of mutant allele of lacI (callled I-) prevents either the production of a repressor polypeptide or produces a polypeptide that cannot bind to the operator sequence. This is also a constitutive expresser of the lac operon because absence of repressor binding permits transcription.

What happens if LacI is mutated?

If the F′prolac contains a mutation in lacI, there will be no repressor activity in the conjugants, and the conjugant will be kanamycin-resistant. On the other hand, if the F′ contains a lacO mutation, it will still produce a functional repressor, and this will prevent expression of the kanamycin resistance gene.

Is LacI part of the lac operon?

One of the major trans-regulators of the lac operon is encoded by lacI. Four identical molecules of lacI proteins assemble together to form a homotetramer called a repressor (Figure 12.1. 2). This repressor binds to two operator sequences adjacent to the promoter of the lac operon.

What is LACL in lac operon?

The lac operon contains three genes: lacZ, lacY, and lacA. These genes are transcribed as a single mRNA, under control of one promoter. Genes in the lac operon specify proteins that help the cell utilize lactose.

Why is the LacI gene expressed without the help of an activator like CRP?

Because RNA polymerase has a high affinity for the PtrpR, the gene is expressed without requiring an activator protein. 26. How does glucose control expression of the lac operon? Low glucose levels increase cAMP levels.

What is the product of the LacI gene?

The operon is regulated by Lac repressor, the product of the lacI gene, which is transcribed from its own promoter (PI). The repressor inhibits transcription by binding to the lac operator (O).

What does LacI bind?

LacI, which is a tetramer, binds to O1 through two of its subunits. The other two subunits then bind either O2 or O3, forming a loop between the operators. Either configuration prevents the binding of RNA polymerase to the promoter.