FIG. 4.

Characterization of Paramecium introns. The GSS introns were identified by inspection of gaps and phase shifts in the BLASTX alignments. The middle part of the figure (B) shows the histogram of intron length for the 462 GSS introns compared to 108 Paramecium introns from the INV division of GenBank. We note that only two of the GSS introns are shorter than 20 nt and consider that experimental validation will be necessary to assert that Paramecium introns can be as small as 18 nt. On the left (A) is shown the consensus sequence at the 5′ exon-intron junction for the GSS introns, and on the right of the histogram (C) is shown the consensus sequence at the 3′ intron-exon junction for the GSS introns. Consensus sequences were calculated at http://www.bio.cam.ac.uk/seqlogo/logo.cgi.