Fig. 7.

RNA-processing enzymes of nidoviruses: possible cooperation and virus distribution. (A) Cellular pathways for processing of pre-U16 small nucleolar RNA (snoRNA) and pre-tRNA splicing in which homologs of five nidovirus RNA-processing enzymes are involved. Note that both pathways produce intermediates with 2′-3′-cyclic phosphate termini (blue circles), indicating the structural basis for a possible cooperation of the nidovirus homologs in a single pathway (Snijder et al., 2003). (B) Table summarizing the conservation of five (putative) RNA-processing enzymes among representatives of large and small nidoviruses. This figure was updated from Fig. 5 presented in Snijder et al. (2003).