Astrovirus has a single-stranded, positive sense, monopartite RNA genome that is approximately 6800 nt in length + a poly-A tail

There are 3 ORFs, ORF-1a, ORF-1b, and ORF-2

ORF-1a

	Encodes the viral protease
	Has a serine protease motif that is similar to other positive-sense RNA proteases
	Astroviruses have a characteristic difference in its protease however.  It has a serine instead of a cystein at the 3rd catalytic amino acid residue
	Has a functional nuclear localization signal.  Astroviruses replicate in the cytoplasm but there might be a nuclear step.  Note that in bovine astrovirus, proteins were found in the nucleus.  The function of this nuclear step in the lifecycle of astrovirus is unknown.

ORF-1b: encodes the RNA-dependent RNA-.  This gene is highly conserved among the 8 astrovirus serotypes

ORF-2

	Encodes the structural proteins.  Having the structural proteins located as such, at the 3' end, is not the typical genomic organization.
	This ORF is present in both the genomic and subgenomic messages, perhaps facilitating sufficient expression of the structural proteins.
	This ORF shows the most sequence variability of the three ORFs.  The N and C termini are highly conserved however.
	It is thought that a single 90 kDa polyprotein is proteolytically cleaved into at least 3 small proteins which then for the capsid.

A 5' UTR precedes ORF-1a by ~ 80 nt.  This length varies with serotype.

ORF-1a overlaps ORF-1b by ~70 nt.  This length also varies with serotype.

Ribosomal frameshift:  There is a (-1) frameshift between ORF-1a and ORF-1b.  There is a conserved heptameric shift sequence A AAA AAC.  This resembles the frameshifting seen in retrovirus protease and polymerase expression and coronavirus polymerase expression.

Some other additional molecular biological characteristics that distinguish astroviruses from caliciviruses and picronaviruses can be found here.

Presently, 5 strains of human astrovirus have been completely sequence.  For you computational biologists, click on the links below to see the sequence.

	Serotype 1, Oxford reference strain.  This strain is maintained in LLCMK2 cells (rhesus monkey kidney epithelial cells.)
	Serotype 1, Newcastle.  Maintained in CaC0-2 cells.  Couldn't find complete sequence.  See link below for more information.
	Serotype 2 Oxford reference strain, maintained in CaC0-2 cells.
	Serotype 3
	Serotype 8