Figure 3

Predicted secondary structure of the B.psf .I1 group II intron from B. pseudofirmus OF4 and comparison of its 3' extension with known domain VIIs. Roman numerals (I to VI) indicate the six typical functional RNA domains. The extra 70-nt 3' segment is boxed in gray. ORF, intron-encoded multifunctional open reading frame. Numbering of residues does not include the ORF. The inset shows a comparison of the secondary structure of the 70-nt 3' extension of B.psf.I1 and the consensus structure of the 53/56-nt domain VII from the 20 other group II introns known to carry a 3' extension (see Table 1; consensus drawn as in ref. [18]). Sites in the B.psf.I1 extension that are identical to the consensus are drawn in a black background. Note the extended S2 stem in B.psf.I1