Coronavirus Properties Genome: have the largest of RNA virus genomes: 30 kB; may represent the upper limit in size. Perhaps because of the error rate and their size, coronaviruses undergo high frequency of recombination. Produce a nested set of mRNAs. Virion Morphology: 120-160 nm, enveloped, nucleocapsids are helical, virion is roughly spherical, not icosahedral Envelope Proteins: Spike protein (S) possesses the receptor binding activity, the fusion activity and is the major determinant for neutralizing antibodies; Membrane protein (M) is an integral membrane protein spanning the membrane 3 times; in some coronaviruses there is an hemaglutinin-esterase (H-E) that is homologous to the influenza C virus H-E Disease: human coronavirus causes colds and perhaps gastroenteritis; in other animals coronaviruses cause gastroenteritis, hepatitis, and a syndrome similar to multiple sclerosis of humans; SARS

Synthesis of Coronavirus RNAs Coronaviruses use a combination of leader-primed transcription and replication of subgenomic mRNAs A leader of ~60 nts can prime the synthesis of subgenomic mRNAs starting at promoters in intergenic regions Subgenomic mRNAs are capable of independent replication once synthesized It is unclear whether leader-primed transcription occurs from the plus strand RNA, the minus strand RNA, or both The relative importance of leader-primed transcription versus independent replication of subgenomic mRNAs may differ in different coronaviruses

The Coronavirus Transmissible Gastroenteritis Virus

Two Murine Coronavirus Genes Suffice for Viral RNA synthesis

Assembled Coronavirus from Complementation of Two Defective Interfering RNAs