RIBOSOMAL FUNCTION IS NECESSARY FOR EFFICIENT SPLICING OF THE T4 PHAGE THYMIDYLATE SYNTHASE INTRON IN-VIVO

Splicing of the group I intron of the T4 thymidylate synthase (td) gen e was uncoupled from translation by introducing stop codons in the ups tream exon. This resulted in severe splicing deficiency in vivo. Overe xpression of a UGA suppressor tRNA partially rescued splicing, suggest ing that this in vitro self-splicing intron requires translation for s plicing in vivo. Inhibition of translation by the antibiotics chloramp henicol and spectinomycin also resulted in splicing deficiency. Riboso mal protein S12, a protein with RNA chaperone activity, and CYT-18, a protein that stabilizes the three-dimensional structure of group I int rons, efficiently rescued the stop codon mutants. We identified a regi on in the upstream exon that interferes with splicing. Point mutations in this region efficiently alleviate the effect of a nonsense codon. We infer from these results that the ribosome acts as an RNA chaperone to facilitate proper folding of the intron.