The multiple origins of human Alu sequences.

I have analyzed a collection of published human Alu sequences. The compiled sequences show several unexpected features, including a uniform pattern of divergence from their consensus sequence, a mutual divergence that is not correlated with their age, and common features in the genomic DNA flanking the 5' ends of the elements. I suggest that the Alu family of sequences derives from a large pool of precursors and not from a single precursor similar to the family consensus sequence, and that new elements integrate into the genome selectively at oligo-A-rich sites.