Fig. 4.

Predicted secondary structures of 16S rRNA gene introns. a Predicted secondary structure of the Pyrobaculum yellowstonensis strain WP30 16S rRNA gene intron at locus 1391, illustrating the highly-structured nature of transcribed intron sequences. Numbers denote nucleotide position along the intron sequence. b-e Predicted secondary structures based on consensus sequences (weblogo) of four different 16S rRNA gene introns. Lower and upper case nucleotides denote 16S rRNA gene sequence and intron sequence, respectively. Arrows indicate hypothesized excision locations (EL) within the bulge-helix-bulge motif