Figure 1. Electron micrograph of Human astrovirus from diarrhoeal faeces. Particles have a smooth margin and display a surface five or six-pointed star motif. Bar, 100 nm.

Figure 2. Proposed cleavage of the astrovirus structural polyprotein. The capsid precursor is produced as a 90 kDa polyprotein, the initial intracellular cleavage is believed to be caspase-mediated, the further cascade of cleavages resulting in the viral structural proteins (indicated in bold type) are carried out extracellularly by the host digestive enzyme (trypsin).

Figure 3. Organization of the human astrovirus genome. Virus RNA is 6800 bases in length, and contains three ORFs. ORFs 1a and 1b are expressed from the full-length virus RNA genome; ORF1b is translated as a 1a–1b fusion following ribosome frameshifting. ORF2 is translated from a subgenomic mRNA formed inside the infected cell. mRNAs are indicated above the coding diagram. Shaded regions indicate the sites of functional motifs identified in the sequence (see text) and the dotted ellipse indicates the site of the –1 frameshifting event.