HE-1 SINE exonization in zebrafish. (a) Alignment of the HE1 SINE from D. rerio and the HE1 SINE from bullhead shark showing the different sections within the transposable element according to . The letters y and r denote pyrimidine and purine, respectively. (b) Non-redundant distribution and orientation of exonized HE1 SINE sequences in which both the 5' and 3' splice sites are within the HE1 SINE sequence. The exonized HE1 SINE sequence regions are aligned against an HE1 SINE consensus element. Each line is a different EST showing exonizations and the box in the middle represents the HE1 element. The number of cases that select that site as a 5' splice site (73, 168, 44) or as a 3' splice site (11, 347) are shown. Exonizations in the sense and antisense orientations are shown above and below the schematic representation of the HE1.