Fig. 6. Model for maturase-promoted RNA splicing. The LtrA protein binds first to its primary binding site DIVa and then makes secondary contacts (arrows) with upstream and downstream regions of the intron to promote folding of the catalytic core. The binding of LtrA to DIVa also positions the protein to initiate cDNA synthesis from a DNA primer in the 3′ exon, as required for intron mobility (Wank et al., 1999).