Coronavirinae

Coronavirinae is a subfamily of viruses in the family Coronaviridae, which are enveloped, positive-sense, single-stranded RNA viruses. They are known for their crown-like appearance under an electron microscope, which is due to the spike glycoproteins on their surface. This subfamily includes several genera, notably Alphacoronavirus, Betacoronavirus, Gammacoronavirus, and Deltacoronavirus.

Structure

Coronaviruses are characterized by their large, spherical virions with bulbous surface projections. The average diameter of a coronavirus particle is around 120 nm. The viral envelope is derived from the host cell membrane and contains the spike (S), membrane (M), and envelope (E) proteins. The spike protein is responsible for attachment to the host cell receptor and is a major determinant of host range and tissue tropism.

Genome

The genome of coronaviruses is a single-stranded RNA, approximately 26 to 32 kilobases in length, which is one of the largest among RNA viruses. The genome is 5' capped and 3' polyadenylated, allowing it to function directly as mRNA for translation of the replicase polyproteins. The replicase gene encodes non-structural proteins that are involved in viral RNA synthesis and processing.

Replication

Coronavirus replication occurs in the cytoplasm of the host cell. After entry into the host cell, the viral RNA genome is released and translated to produce the replicase polyproteins. These polyproteins are cleaved by viral proteases to form the replication-transcription complex. This complex synthesizes a full-length negative-sense RNA template, which is used to produce new genomic RNA and subgenomic mRNAs. The subgenomic mRNAs encode the structural proteins, which are translated and assembled into new virions in the endoplasmic reticulum-Golgi intermediate compartment (ERGIC).

Pathogenicity

Coronaviruses can infect a variety of hosts, including humans, birds, and mammals. In humans, they are known to cause respiratory infections ranging from the common cold to more severe diseases such as Severe Acute Respiratory Syndrome (SARS), Middle East Respiratory Syndrome (MERS), and COVID-19. The severity of the disease depends on the specific virus and the host's immune response.

Epidemiology

Coronaviruses are zoonotic, meaning they can be transmitted between animals and humans. The emergence of new coronavirus strains is often associated with cross-species transmission events. Human coronaviruses are typically spread through respiratory droplets, direct contact, and fomites.

Also see

• Coronaviridae
• SARS-CoV-2
• Viral replication
• RNA virus