Contains the viral protease participating in the cleavage of the polyprotein into functional products. Protein covalently attached to the 5' extremity of the genomic and subgenomic RNAs. a ribonucleoside 5'-triphosphate + RNA(n) = diphosphate + RNA(n+1) Cleaved presumably by viral and host proteases. Belongs to the astroviridae polyprotein 1A family.