Conservation of intron boundary sequences in Giardia lamblia , Trichomonas vaginalis and Carpediemonas membranifera . Positions of nucleotide identity within the intron sequences in G. lamblia and C. membranifera are indicated with asterisks. Potential intron branch-point sequences are underlined. The distance between the intron boundary sequences is indicated for each G. lamblia intron as is the distance variation between these sequences seen in the T. vaginalis introns used to derive the consensus sequence shown. The ferredoxin intron sequence is from , the T. vaginalis introns are from , and the carbamate kinase intron sequences are from .