Gene cassette
Encyclopedia
A gene cassette is broadly a modular DNA sequence
encoding one or more genes for a single biochemical function.
In genetic engineering
, a gene cassette refers to a manipulable fragment of DNA carrying, and capable of expressing, one or more genes of interest between one or more sets of restriction sites
. It can be transferred from one DNA sequence (usually on a vector) to another by 'cutting' the fragment out using restriction enzymes and 'pasting' it back into the new context.
Integrons are genetic structures in bacteria
which express and are capable of acquiring and exchanging 'gene cassettes'. These cassettes typically carry a single gene without a promoter. The entire series of cassettes is transcribed
from an adjacent promoter. The gene cassettes are speculated to be inserted and excised via a circular
intermediate. This would involve recombination between short sequences found at their termini and known as 59 base elements (59-be) - which may not be 59 bases long. The 59-be are a diverse family of sequences that function as recognition sites for the site-specific integrase (enzyme responsible for integrating the gene cassette into an integron).
Gene cassettes often carry antibiotic resistance
gene
s. An example would be the kanMX cassette which confers kanamycin
(an antibiotic
) resistance upon bacteria
or fungi.
How these cassettes are initially created is not clear.
In the case of the ATP-binding cassette transporter, the cassette is made of the Q-loop, his-loop, pro-loop and the D-loop
.
STOP Cassette - integrates a stop codon
DNA sequence
The sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...
encoding one or more genes for a single biochemical function.
In genetic engineering
Genetic engineering
Genetic engineering, also called genetic modification, is the direct human manipulation of an organism's genome using modern DNA technology. It involves the introduction of foreign DNA or synthetic genes into the organism of interest...
, a gene cassette refers to a manipulable fragment of DNA carrying, and capable of expressing, one or more genes of interest between one or more sets of restriction sites
Restriction sites
Restriction sites, or restriction recognition sites, are locations on a DNA molecule containing specific sequences of nucleotides, which are recognized by restriction enzymes...
. It can be transferred from one DNA sequence (usually on a vector) to another by 'cutting' the fragment out using restriction enzymes and 'pasting' it back into the new context.
Integrons are genetic structures in bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
which express and are capable of acquiring and exchanging 'gene cassettes'. These cassettes typically carry a single gene without a promoter. The entire series of cassettes is transcribed
Transcription (genetics)
Transcription is the process of creating a complementary RNA copy of a sequence of DNA. Both RNA and DNA are nucleic acids, which use base pairs of nucleotides as a complementary language that can be converted back and forth from DNA to RNA by the action of the correct enzymes...
from an adjacent promoter. The gene cassettes are speculated to be inserted and excised via a circular
Circular DNA
Circular DNA is a form of DNA that is found in viruses, bacteria and archaea as well as in eukaryotic cells in the form of either mitochondrial DNA or plastid DNA....
intermediate. This would involve recombination between short sequences found at their termini and known as 59 base elements (59-be) - which may not be 59 bases long. The 59-be are a diverse family of sequences that function as recognition sites for the site-specific integrase (enzyme responsible for integrating the gene cassette into an integron).
Gene cassettes often carry antibiotic resistance
Antibiotic resistance
Antibiotic resistance is a type of drug resistance where a microorganism is able to survive exposure to an antibiotic. While a spontaneous or induced genetic mutation in bacteria may confer resistance to antimicrobial drugs, genes that confer resistance can be transferred between bacteria in a...
gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
s. An example would be the kanMX cassette which confers kanamycin
Kanamycin
Kanamycin sulfate is an aminoglycoside antibiotic, available in oral, intravenous, and intramuscular forms, and used to treat a wide variety of infections. Kanamycin is isolated from Streptomyces kanamyceticus.-Mechanism:...
(an antibiotic
Antibiotic
An antibacterial is a compound or substance that kills or slows down the growth of bacteria.The term is often used synonymously with the term antibiotic; today, however, with increased knowledge of the causative agents of various infectious diseases, antibiotic has come to denote a broader range of...
) resistance upon bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
or fungi.
How these cassettes are initially created is not clear.
In the case of the ATP-binding cassette transporter, the cassette is made of the Q-loop, his-loop, pro-loop and the D-loop
D-loop
In molecular biology, a displacement loop or D-loop is a DNA structure where the two strands of a double-stranded DNA molecule are separated for a stretch and held apart by a third strand of DNA. The third strand has a base sequence which is complementary to one of the main strands and pairs with...
.
STOP Cassette - integrates a stop codon