Fig. 3.

Examples of introns flanked by direct repeats. (A) Partial sequence alignment of DNA pol α genes from seven spirotrichs (U. grandis, Holosticha sp., Uroleptus sp., P. weissei, S. lemnae, S. nova, and S. histriomuscorum) surrounding the 3′ intron of this gene in Uroleptus. Confirmed intron sequences are shown in lowercase and italics. The 168-/198-bp putative 3′ intron in U. grandis (see text) is shown in lowercase. Direct repeats flanking introns are highlighted, and pointer sequences are underlined. The product after hypothetical IES splicing in U. grandis is six nucleotides longer than the product after putative intron removal; thus, the reading frame would be preserved. The phylogeny on the left is from Fig. 1. (B) Sequence surrounding the first 5′ intron in three species. Products after intron removal in these three cases would be identical to products after hypothetical IES splicing.