Notes on Genus: Deltacoronavirus

enveloped spheres

Type member: Bulbul coronavirus HKU11

General Description

This is one of the genera in the subfamily Coronavirinae of the family Coronaviridae. Within this subfamily, viruses have spherical virions with club-shaped surface projections and a core shell. The name is from the Latin corona = crown, reflecting the appearance of these projections in electron microscopy. This genus contains viruses infecting birds.

Morphology

Virions enveloped and spherical 120-160 nm in diameter, with a core shell of about 65nm. The large surface projections are formed by glycoproteins and a trimers of the spike protein.

Genome

Monopartite positive sense single-stranded RNA 26-27 kb in length and with a 3'-polyA tail.

Genus Genomic Organization

Two large, overlapping ORFs at the 5'-end of the genome encode the major non-structural proteins and are expressed as a fusion protein by ribosomal frameshift. These contain regions with protease, helicase and RNA polymerase motifs. Downstream are up to 8 other genes, most of which encode structural proteins, and these are expressed from a 3'-coterminal nested set of subgenomic RNAs. The major characterised proteins occur in a conserved order and are:

Spike protein S
Small envelope protein E
Membrane protein M
Non-structural protein 6
Coat protein N
Three small non-structural protein downstream of N (designated 7a, 7b and 7c)

Type Member Genomic Organization

The RNA of 26.5 kb is translated into the following products:

Replication fusion protein 1a-1b of 699 kDa
Spike protein S of128 kDa
Small envelope protein E of 9.3 kDa
Membrane protein M of 26 kDa
Non-structural protein 6 of 10.5 kDa
Coat protein N of 38.2 kDa
Non-structural protein 7a of 13.9 kDa
Non-structural protein 7b of 9.4 kDa
Non-structural protein 7c of 11.2 kDa