A NEW RETROTRANSPOSABLE HUMAN L1 ELEMENT FROM THE LRE2 LOCUS ON CHROMOSOME 1Q PRODUCES A CHIMERIC INSERTION

We have found a 2 kilobase insertion containing a rearranged L1 elemen t in the dystrophin gene of a muscular dystrophy patient. We cloned th e precursor of this insertion, the second known active human L1 elemen t. The locus, LRE2, has one allele derived from the patient which matc hes the insertion sequence exactly. LRE2 has a perfect 13-15 bp target site duplication, two open reading frames, and an unusual 21 bp trunc ation of the 5' end, suggesting that a slightly truncated element can still retrotranspose. It differs from LRE1 by similar to 0.7%. There i s an L1 element at LRE2 on similar to 66% of human chromosomes 1q, and the element is absent from chimpanzee and gorilla genomes. These data demonstrate that multiple active L1 elements exist in the human genom e, and that a readthrough transcript of an active element is capable o f retrotransposition.