cDNA libraries from porcine group (Gp) C rotavirus strain Cowden and a human Gp C rotavirus strain were generated. The complete nucleotide sequence of gene 8 from the Cowden strain was determined from gene 8-specific clones and viral transcript RNA. A full-length gene 8 clone was generated from the human Gp C virus by polymerase chain reaction (PCR) using primers deduced from the 3' and 5' ends of the Cowden strain gene 8, and the sequence of the human Gp C gene 8 was determined from this clone and gene 8 clones in the cDNA library. The gene 8 from the Cowden or the human Gp C strain is 1063 nucleotides in length and contains a long open reading frame beginning at the 49th nucleotide from the 5' end and terminating with a stop codon 16 bases from the 3' end. The encoded protein contains 332 amino acids (predicted molecular weight of 37.3 kDa) with two potential N-linked glycosylation sites in the porcine strain and three in the human strain. The polypeptide products derived from in vitro translation of the transcript RNA generated from a porcine gene 8 clone containing the entire open reading frame were analogous in size with the Gp A VP7. The gene 8 of porcine and human Gp C rotaviruses exhibited considerable nucleotide and deduced amino acid sequence identity (83.8 and 88.0%, respectively). Comparison of the Gp C gene 8 protein sequence with the VP7 protein of Gp A rotavirus revealed structural similarities, although the overall amino acid identity was low (less than 30%). These data suggest that the gene 8 of the porcine or human Gp C rotavirus encodes a protein corresponding to the VP7 outer capsid glycoprotein of Gp A rotaviruses and that the eighth gene is highly conserved in the porcine and human Gp C strains examined in this study.