FIG. 2.

Putative interactions between exon and intron sequences. (a) Comparison of structures of the putative interaction found in nrdB and the interaction found to interfere with td splicing (31). Exon sequences are in uppercase letters, and intron sequences in lowercase letters. An arrow indicates the 3′ splice site. Distance between exon and intron regions in the two experimental systems is indicated. (b and c) Putative cryptic P1 pairings in the nrdB and nrdD introns. Exon sequences are in uppercase letters, and intron sequences are in lowercase letters. Arrows indicate the 5′ splice sites. The naturally occurring stop codon at the start of each intron is marked with a box and the extent of the ΔCry-P1 deletion in nrdB is indicated.