Sequences and base-pairing interactions of the U6/U6atac snRNA chimeras Mod-1 and Mod-2 with the modified U4atac snRNA. (A) The U6 Mod-1 chimera consists of U6 nucleotides 1–79 joined to U6atac nucleotides 52–125 (3′ stem–loop region shown within the box). The U6 nucleotides U40, A41, and C42 are also replaced by the sequence AACC, which base pairs to the mutant U12-dependent 5′ splice site in the P120 intron F minigene. The modified U4atac snRNA is shown base paired to the U6 portion of the chimera due to the changes shown in bold in the stem II region. (B) The U6 Mod-2 chimera consists of U6atac nucleotides 1–22 joined to U6 nucleotides 51–108 (as shown in the box). The U6atac sequence includes the GG14/15CC mutation that suppresses the CC5/6GG mutation in the P120 minigene construct. Also shown is the modified U4atac snRNA base paired to the U6 snRNA region of the chimera.
