Module 02 - Section 06 Flashcards
What is Site-Specific Recombination?
Precise and predicable process in which DNA is rearranged between 2 specific sequences.
Involves the movement of specialized nucleotide sequences called mobile genetic elements between non-homologous sites
What are mobile genetic elements
DNA sequences that can move around the genome changing either their number of copies or location. They include transposable elements, plasmids, and bacteriophage elements
What are the effects of Site-Specific recombination?
- Can alter gene order, this process is used to regulate gene expression and to increase the organisms’s genetic repertoire
- Can give rise to spontaneous mutations in organisms
What are some biotechnological applications of Site-Specific Recombination?
Activate a particular gene, insert a new gene into a cell at a chosen location, and replace one gene with another gene or an altered version of the same gene, delete a gene or alter the linear structure of an entire chromosomes
- Know-out mice and knock-in mice (deletion or adding of a gene to study its effect)
What are the two systems that use site-specific recombination for genome editing?
Cre-Lox
Flp-FRT
Cre-LoxtP and Flp-FRT systems; what are LoxP and FRT?
Specific directional sequences that are placed in the genome – but are NOT naturally occurring in the genome
Cre-LoxtP and Flp-FRT systems; what are Cre and Flp?
Recombinase enzymes that recognize the LoxP and FRT sites – also NOT naturally occurring in eukaryotes
What is the importance of the orientation of the LoxP or FRT sites?
(1) Inverted (facing towards each other); recombinase will invert the intervening sequence, changing its orientation on the DNA
(2) If sites are oriented in the same direction; recombinase can cleave out the intervening sequence, leaving behind one perfectly reformed LoxP or FRT site
Name an application of the Cre-LoxP system?
Brainbow technology: visualization of using fluorescent proteins to mal all then neurons in a mouse brain
Describe the method of the brainbow technique
(1) Gene cassette with several copies of GFP variants that encode proteins fluorescing with different colors
(2) Variants of the LoxP site for the Cre recombinase are engineered between the genes - different lox sites differ in their core sequences so lox1 only react with lox1, lox2 with lox2 ,etc..
(3) Cassette utilizes 3 or more different lox sites so that Cre-mediated recombination results in different patterns of GFP varian expression and thus a different colour in each neuron
(4) Cassette also includes a promoter that directs gene expression only in neurons
What is the outcome of Brainbow?
A mouse with GFP cassettes mates with a mouse expressing Cre recombinase, their progeny are heterozygous. Recombination events, occur, 1 type per cel= particular colour. Result= rainbow like array of fluorescent colours in the neural network to trace paths of axons
How are the different lox sites prevented from recombining with each other?
Core sequence must be modified to prevent recombination between the different loxP sites
What is one of the main methods molecular biologists use to understand gene function?
Delete it – then examine effects of an absence of a protein on the cell function and infer the gene product’s function
What are the 3 technologies that have been developed to cut genes at particular sites in vivo?
(1) Zinc Finger nucleases
(2) TALENs
(3) CRISPR/Cas systems
What is a zinc finger?
protein domain characterized by a single atom of zinc coordinated to four Cys residues or 2 His and 2 Cyz residues. It’s about 30 amino acids and folds in a beta sheet-alpha helix-beta-sheet structure aided by a Zn2+ ion
