What does the lacI gene code for?
What does the lacI gene code for?
The structural gene for the lac repressor of Escherichia coli, the lacI gene has been sequenced. This 1,080 base pair region of the E. coli chromosome codes for the lac repressor protein of 360 amino acids.
How does lacI work?
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 happens if lacI is mutated?
A mutation in the lacI gene results in the expression of β-galactosidase. Besides galactose, which is its normal substrate, this enzyme can also cleave X-gal.
What type of gene is lacI?
However, the lacI gene (regulatory gene for lac operon) produces a protein that blocks RNAP from binding to the operator of the operon. This protein can only be removed when allolactose binds to it, and inactivates it. The protein that is formed by the lacI gene is known as the lac repressor.
What is a major disadvantage to a bacterial cell of having an operon?
What is a major disadvantage to a bacterial cell of having an operon? If there is a mutation in a regulatory region, none of the proteins will be synthesized.
Where are two alleles of a gene located?
genetic locus
An allele is a variant form of a gene. Some genes have a variety of different forms, which are located at the same position, or genetic locus, on a chromosome. Humans are called diploid organisms because they have two alleles at each genetic locus, with one allele inherited from each parent.
Is lac an operon?
The lac operon is an operon, or group of genes with a single promoter (transcribed as a single mRNA). The genes in the operon encode proteins that allow the bacteria to use lactose as an energy source.
What happens if lac operon is mutated?
Cells carrying these mutations also cannot induce expression of the lacY and lacA genes; that is, these mutations prevent expression of the entire lac operon. According to the Jacob and Monod model, such promoter mutations block initiation of transcription by RNA polymerase (see Figure 10-2).
Are non functional repressor alleles dominant or recessive?
Non-functional repressor alleles are recessive, because the repressor made by the functional lacI can act on any copy of the operon.
What is the most important reason a cell exhibits tight?
What is the MOST important reason a cell exhibits tight transcriptional control over the regulation of gene expression? Regulation at the transcriptional level is energetically efficient for the cell.
What is the lac operon model?
What is the purpose of the lacI gene?
The lacI gene: The lacI gene of the lac operon has been used extensively for the recovery and analysis of mutations in bacteria with various DNA repair backgrounds and after exposure to a wide variety of mutagens.
Which is the structural gene for the lac repressor?
The structural gene for the lac repressor of Escherichia coli, the lacI gene has been sequenced. This 1,080 base pair region of the E. coli chromosome codes for the lac repressor protein of 360 amino acids. The DNA sequence largely confirms but extends the previously reported protein sequence and allows a structural analysis of genetic phenomena.
Which is lacI-lactose operon repressor in Escherichia coli?
“A complexomic study of Escherichia coli using two-dimensional blue native/SDS polyacrylamide gel electrophoresis.” “Tetramer opening in LacI-mediated DNA looping.” “Phylogenetic-based propagation of functional annotations within the Gene Ontology consortium.” Complete GO annotation on QuickGO “Mutants that make more lac repressor.”
What happens when LacI protein is unable to form a tetramer?
When mutant LacI protein is unable to form a tetramer and bind the operator, transcription of the lacZ gene occurs. In most constructs, an amino-terminal fragment, or an α-lacZ fragment, is produced. This fragment may complement a carboxy-terminal or omega fragment that is provided by an appropriate host cell.
