Bacteriophage Qβ
Encyclopedia
Bacteriophage Qβ is an icosahedral virus
with a diameter of 25 nm. Its host is Escherichia coli
. Qβ enters its host cell through the side of the F pilus.
of Qβ is 4218 nucleotides long. The genome has three open reading frame
s and encodes four protein
s: A1, A2, CP and qβ replicase. The genome is highly structured, which regulates gene expression and protects the genome from host RNases.
; A2 inhibits the formation of peptidoglycan
by inhibiting the enzyme UDP-N-acetylglucosamine 1-carboxyvinyltransferase
(MurA), which catalyzes the first committed step of peptidoglycan synthesis.
A2 also functions in host cell recognition and cell entry. When A2 binds to the sex pilus of the bacterium, A2 cleaves and forms a pore into the host.
), and delta subunit (EF-Ts
).
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
with a diameter of 25 nm. Its host is Escherichia coli
Escherichia coli
Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...
. Qβ enters its host cell through the side of the F pilus.
Genetics
The genomeGenome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
of Qβ is 4218 nucleotides long. The genome has three open reading frame
Open reading frame
In molecular genetics, an open reading frame is a DNA sequence that does not contain a stop codon in a given reading frame.Normally, inserts which interrupt the reading frame of a subsequent region after the start codon cause frameshift mutation of the sequence and dislocate the sequences for stop...
s and encodes four protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
s: A1, A2, CP and qβ replicase. The genome is highly structured, which regulates gene expression and protects the genome from host RNases.
Protein A2
A2 is called the maturation protein due to its lysis activity. One copy of A2 is present per virion. The mechanism of lysis is similar to that of penicillinPenicillin
Penicillin is a group of antibiotics derived from Penicillium fungi. They include penicillin G, procaine penicillin, benzathine penicillin, and penicillin V....
; A2 inhibits the formation of peptidoglycan
Peptidoglycan
Peptidoglycan, also known as murein, is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of bacteria , forming the cell wall. The sugar component consists of alternating residues of β- linked N-acetylglucosamine and N-acetylmuramic acid...
by inhibiting the enzyme UDP-N-acetylglucosamine 1-carboxyvinyltransferase
UDP-N-acetylglucosamine 1-carboxyvinyltransferase
In enzymology, an UDP-N-acetylglucosamine 1-carboxyvinyltransferase is an enzyme that catalyzes the chemical reactionThus, the two substrates of this enzyme are phosphoenolpyruvate and UDP-N-acetyl-D-glucosamine, whereas its two products are phosphate and UDP-N-acetyl-3-O--D-glucosamine.This...
(MurA), which catalyzes the first committed step of peptidoglycan synthesis.
A2 also functions in host cell recognition and cell entry. When A2 binds to the sex pilus of the bacterium, A2 cleaves and forms a pore into the host.
RNA Polymerase
The RNA polymerase that replicates both the plus and minus RNA strands is a complex of four proteins: the beta subunit (replicase) is encoded by the phage, while the other three subunits are encoded by the bacterial genome: alpha subunit (ribosomal protein S1), gamma subunit (EF-TuEF-Tu
EF-Tu is one of the prokaryotic elongation factors.The prokaryotic factor EF-Tu mediates the entry of the aminoacyl-tRNA into a free site of the ribosome. EF-Tu functions by binding an aminoacylated, or charged, tRNA molecule in the cytoplasm...
), and delta subunit (EF-Ts
EF-Ts
EF-Ts is one of the prokaryotic elongation factors.EF-Ts serves as the guanine nucleotide exchange factor for EF-Tu , catalyzing the release of guanosine diphosphate from EF-Tu...
).