Parameters used to determine the length of the A-tail of an Alu element. Alu elements (solid bar) and their A-tails are flanked by direct repeats (arrows) that are created during their insertion into the genome. For this study, the length of the A-tail was considered as the number of bases between the last nucleotide of the Alu consensus sequence and the 3′ flanking direct repeat. If the direct repeat sequence contained adenosine residues in its 5′ end, they were included in the count. The A-tail length for long interspersed elements (LINES) was determined by counting the number of bases between the last nucleotide of the L1 consensus until reaching two consecutive non-adenosine bases, unless another poly(A) stretch followed. In the example, the A-tail length would be considered to be 9 for the Alu and 10 for the LINE. Note that the A-tails may contain other nucleotide residues.
