Caliciviridae Molecular Biology

A summary of the key genomic features of caliciviruses

 

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Nidhi Bhat

Stanford University

Class of 2008 

 

Genomic organization

The calicivirus genome is organized into three open reading frames: ORF1, ORF2 and ORF 3. ORF1 encodes the nonstructural proteins of the virus: the helicase, protease and polymerase. ORF2 encodes the single structural protein of the capsid. ORF3 is the smallest open reading frame at the 3' terminus of the genome, and encodes a basic structural protein of unknown function!

Transcription and translation

Transcription produces two RNA transcripts: one genomic and one subgenomic mRNA. This transcriptional strategy differentiates caliciviruses from picornaviruses, with which they were originally classified. Translation involves the cleavage of the virus polyprotein, which was transcribed from ORF1. This large polyprotein is cleaved by proteases into the three nonstructural proteins mentioned above.

Other features of the genome

Calicivirus RNA features a VPg protein, bound to the 5' end of both genomic and subgenomic mRNA. The VPg protein likely functions as a nonstructural protein during replication, but its function has not been confirmed.

Calicivirus RNA is also unique because it is polyadenylated (features a 3'polyA tail). The polyA tail is important for transcription termination and translation.

 

Calicivirus genome with three open reading frames. (PATRIC)