Schematic alignment of tomato RdRP with proteins known to be involved in PTGS in fungus (QDE-1), nematodes (EGO-1), and plants (SGS2/SDE1). The region that is conserved among all four proteins is shaded. The total number of amino acids in each protein is listed to the right; amino acid positions delimiting the conserved regions are indicated. Within the shaded region, the percentage of RdRP amino-acid sequence identical to each related gene sequence is as follows: QDE-1, 17%; EGO-1, 25%; SDS2/SDE1, 41%. Sequence blocks of higher identity are scattered within the shaded region. Substantial sequence similarity between RdRP and SGS2/SDE1 is present in the non-shaded region as well; QDE-1 is relatively divergent from the other three proteins.