Figure 2

Combined positional frequencies of selected groups of tetramers downstream of the 3'-processing site for ten metazoan species. A: Proximal UG-rich element (including UGUG and GUGU), B: distal U-rich element (including all single base substitutions of UUUU), C: alternative proximal UG-rich element with G to C transversion (including UCUG, CUGU, UGUC, and GUCU) and D: G rich element (including GGGG, GGGA, GGAG, GAGG, and AGGG). In all panels, the vertical axis is the frequency of occurrence of any of the grouped tetramers at the position indicated along the horizontal axis.