RB1 and osteosarcoma: We coexpressed MmuPV1 E7 with plasmids expressing full-length RB1 (amino acid residues 1 to 928) or truncation mutants of RB1 lacking the amino terminus (amino acid residues 379 to 928) or the C terminus (amino acid residues 1 to 792) in SAOS2 human osteosarcoma cells.