The Infectious bronchitis virus D-RNA is an RNA element known as defective

RNA Ribonucleic acid (RNA) is a polymeric molecule that is essential for most biological functions, either by performing the function itself (non-coding RNA) or by forming a template for the production of proteins (messenger RNA). RNA and deoxyrib ...

or D-RNA. This element is thought to be essential for

viral replication Viral replication is the formation of biological viruses during the infection process in the target host cells. Viruses must first get into the cell before viral replication can occur. Through the generation of abundant copies of its genome ...

and efficient packaging of avian infectious bronchitis virus (IBV) particles.

Coronavirus Coronaviruses are a group of related RNA viruses that cause diseases in mammals and birds. In humans and birds, they cause respiratory tract infections that can range from mild to lethal. Mild illnesses in humans include some cases of the comm ...

D-RNA like that of IBV, are produced during high

multiplicity of infection In microbiology, the multiplicity of infection or MOI is the ratio of agents (e.g. phage or more generally virus, bacteria) to infection targets (e.g. cell). For example, when referring to a group of cells inoculated with virus particles, the MO ...

and contain ''cis-''acting sequences which are required for viral replication. While it is unclear exactly how IBV D-RNA is made, it is thought to be synthesized in a similar manner as subgenomic mRNA (sg mRNA), with most of the genomic sequence left out of the product. Additionally, sg mRNA can also be synthesized from the IBV D-RNA, although the mechanism of that process is still largely unknown. IBV D-RNA is often used in the reverse genetics approach to experimentally induce heterologous gene expression and site-specific

mutagenesis Mutagenesis () is a process by which the genetic information of an organism is changed by the production of a mutation. It may occur spontaneously in nature, or as a result of exposure to mutagens. It can also be achieved experimentally using lab ...

of the coronavirus genome. However, a translation associated sequence (TAS), which is normally used to transcribe sg mRNA and is derived from gene 5 of the Beaudette strain of IBV, is needed as a promoter to regulate heterologous gene expression. It is also thought that TAS may program some IBV D-RNA to synthesize sg mRNA, which are necessary for homologous gene protein synthesis. In particular, IBV D-RNA CD-61 is used to experimentally produce recombinant IBV

vaccine A vaccine is a biological Dosage form, preparation that provides active acquired immunity to a particular infectious disease, infectious or cancer, malignant disease. The safety and effectiveness of vaccines has been widely studied and verifi ...

s. D-RNA CD-61 was created from the naturally occurring IBV D-RNA CD-91, which is produced by multiple passage of high concentration IBV in chick kidney (CK) cells. The IBV D-RNA CD-61 resulted from deletion mutagenesis of CD-91 and lacks much of the genome but retains the sequences necessary for replication and packaging of viral particles in the presence of a helper virus. One particularly promising method of IBV D-RNA-mediated heterologous gene expression uses the helper virus dependent system to promote IBV immunity. The helper virus identifies and responds to signals within the IBV D-RNA that are responsible for replication and packaging of IBV particles. Those sequences are thought to be contained within the 5’ and 3’ UTRs of the D-RNA. Analysis of the packaged IBV particles revealed that leader sequence switching occurs between the D-RNA and the IBV helper viruses, which was similarly observed in bovine coronavirus. In addition, it was found that the TAS of the IBV D-RNA contained a

consensus sequence In molecular biology and bioinformatics, the consensus sequence (or canonical sequence) is the calculated sequence of most frequent residues, either nucleotide or amino acid, found at each position in a sequence alignment. It represents the result ...

that can accept the switched leader sequence and can also be involved in the expression of

mRNA In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of Protein biosynthesis, synthesizing a protein. mRNA is ...

from D-RNA. With the helper virus dependent system, chIFN-gamma-containing IBV D-RNA was successfully used to induce the expression of chicken gamma interferon in IBV-infected CK cells to produce possible immunity against avian IBV, which is a highly infectious

pathogen In biology, a pathogen (, "suffering", "passion" and , "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a Germ theory of d ...

of chickens that causes respiratory, reproductive, and growth complications. It was also shown that biologically active chIFN-gamma was secreted into the allantonic fluid of chicken embryos ''

in vivo Studies that are ''in vivo'' (Latin for "within the living"; often not italicized in English) are those in which the effects of various biological entities are tested on whole, living organisms or cells, usually animals, including humans, an ...

,'' showing that induction of

cytokine Cytokines () are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling. Cytokines are produced by a broad range of cells, including immune cells like macrophages, B cell, B lymphocytes, T cell, T lymphocytes ...

s and, therefore, an immune response, can be induced in living organisms in addition to cultured cells. The use of IBV D-RNA as a

vector Vector most often refers to: * Euclidean vector, a quantity with a magnitude and a direction * Disease vector, an agent that carries and transmits an infectious pathogen into another living organism Vector may also refer to: Mathematics a ...

to create vaccines for IBV is of economic significance. Due to the IBV tropism which specifically targets chickens, recombinant IBV vaccines may provide economical security for poultry farms responsible for egg and meat production around the world.

References

External links

* {{Rfam, id=RF00385, name=Infectious bronchitis virus D-RNA Cis-regulatory RNA elements Gammacoronaviruses

See also

References

External links