-!- Viruses that are members of the Norovirus genus (Caliciviridae family) are a major cause of epidemic acute viral gastroenteritis. -!- The nonstructural proteins of these viruses are produced by proteolytic cleavage of a large precursor polyprotein, performed by a protease that is incorporated into the polyprotein. -!- Cleavage sites are apparently defined by features based on both sequence and structure since several sites in the polyprotein fulfilling the identified sequence requirements are not cleaved. -!- The presence of acidic (Asp), basic (Arg), aromatic (Tyr) or aliphatic (Leu) amino acids at the P1' position results in only minor differences in cleavage efficiency, suggesting that steric or conformational constraints may play a role in determining specificity. -!- Changes to the amino acid at the P2 position do not alter cleavage efficiency. -!- Belongs to peptidase family C37.

-!- The enzyme is found in eukaryotes and thermophilic bacteria, but appears to be absent from mesophilic bacteria. -!- Also hydrolyzes nucleoside diphosphates, thiamine diphosphate and FAD. -!- The enzyme from the plant Pisum sativum (garden pea) is regulated by calmodulin.

-!- Catalyzes RNA-template-directed extension of the 3'-end of an RNA strand by one nucleotide at a time. -!- Can initiate a chain de novo. -!- See also EC 2.7.7.6.