Methyltransferase displays a cytoplasmic capping enzyme activity. This function is necessary since all viral RNAs are synthesized in the cytoplasm, and host capping enzymes are restricted to the nucleus. The enzymatic reaction involves a covalent link between 7-methyl-GMP and the methyltransferase, whereas eukaryotic capping enzymes form a covalent complex only with GMP. Methyltransferase catalyzes transfer of a methyl group from S-adenosylmethionine to GTP and GDP to yield m(7)GTP or m(7)GDP. GMP, GpppG, and GpppA were poor substrates for the methyltransferase. This enzyme also displays guanylyltransferase activity to form a covalent complex, methyltransferase-m(7)GMP, from which 7-methyl-GMP is transferred to the mRNA to create the cap structure. Cap analogs such as m(7)GTP, m(7)GDP, et(2)m(7)GMP, and m(2)et(7)GMP inhibit the methyltransferase reaction (By similarity). RNA-directed RNA polymerase plays an essential role in the virus replication. Binds to the 3'-end of the genomic RNA, probably to initiate replication (By similarity). Helicase region exhibits NTPase and RNA unwinding activities. a ribonucleoside 5'-triphosphate + RNA(n) = diphosphate + RNA(n+1) It is not yet clear whether the ORF1-encoded polyprotein contains multiple biochemical activities, or undergoes cis or trans- processing to release biochemically distinct peptides. Belongs to the hepevirus non-structural polyprotein family.