Figure 8

Motif location frequency around polyadenylation [poly(A)] sites. The frequency (%) is the percentage of mRNAs that have the motif’s first nucleotide starting from the position. The UUACUU motif in Trypanosoma cruzi started at position −2 [with the nucleotide A directly at the poly(A) site]. The UGUAAC motif in Chlamydomonas reinhardtii was at position −18 [i.e., the poly(A) site and the motif’s last base were separated by 12 bases]. The UGUUUG motif in Blastocystis hominis was located at downstream position 5--the poly(A) tail attachment position and the motif’s first base were separated by four bases [i.e., the poly(A) site and the motif were separated by three bases]. The UAUUUU motif in Medicago truncatula had a peak value at position −1, with the nucleotide A of the motif located at the poly(A) site, but the motif was not concentrated at one location. The AAUAAA motif had its peak value at position −21 in human and most animals, position −22 in Arabidopsis (data not shown), and position −24 in maize (but the peak was weak). Note that each of the predominant motifs was found to occur usually at a specific location, whether upstream of, at, or downstream of the poly(A) site. The AAUAAA motif corresponded to the A-rich upstream region in both maize (representing the plant kingdom) and human (representing the animal kingdom), and the location of AAUAAA was highly conserved, with a difference of a few bases between plants and animals.